ramips: add support for Amped Wireless ALLY router and extender

ramips: add support for Amped Wireless ALLY router and extender

Amped Wireless ALLY is a whole-home WiFi kit, with a router (model
ALLY-R1900K) and an Extender (model ALLY-00X19K).  Both are devices are
11ac and based on MediaTek MT7621AT and MT7615N chips.  The units are
nearly identical, except the Extender lacks a USB port and has a single
Ethernet port.

Specification:
- SoC: MediaTek MT7621AT (2C/4T) @ 880MHz
- RAM: 128MB DDR3 (Nanya NT5CC64M16GP-DI)
- FLASH: 128MB NAND (Winbond W29N01GVSIAA)
- WiFi: 2.4/5 GHz 4T4R
  - 2.4GHz MediaTek MT7615N bgn
  - 5GHz MediaTek MT7615N nac
- Switch: SoC integrated Gigabit Switch
- USB: 1x USB3 (Router only)
- BTN: Reset, WPS
- LED: single RGB
- UART:  through-hole on PCB.
   J1: pin1 (square pad, towards rear)=3.3V, pin2=RX,
   pin3=GND, pin4=TX.  Settings: 57600/8N1.

Note regarding dual system partitions
-------------------------------------

The vendor firmware and boot loader use a dual partition scheme.  The boot
partition is decided by the bootImage U-boot environment variable: 0 for
the 1st partition, 1 for the 2nd.

OpenWrt does not support this scheme and will always use the first OS
partition.  It will set bootImage to 0 during installation, making sure
the first partition is selected by the boot loader.

Also, because we can't be sure which partition is active to begin with, a
2-step flash process is used.  We first flash an initramfs image, then
follow with a regular sysupgrade.

Installation:

Router (ALLY-R1900K)
1) Install the flashable initramfs image via the OEM web-interface.
  (Alternatively, you can use the TFTP recovery method below.)
  You can use WiFi or Ethernet.
  The direct URL is:  http://192.168.3.1/07_06_00_firmware.html
  a. No login is needed, and you'll be in their setup wizard.
  b. You might get a warning about not being connected to the Internet.
  c. Towards the bottom of the page will be a section entitled "Or
  Manually Upgrade Firmware from a File:" where you can manually choose
  and upload a firmware file.
  d: Click "Choose File", select the OpenWRT "initramfs" image and click
  "Upload."
2) The Router will flash the OpenWrt initramfs image and reboot.  After
  booting, LuCI will be available on 192.168.1.1.
3) Log into LuCI as root; there is no password.
4) Optional (but recommended) is to backup the OEM firmware before
  continuing; see process below.
5) Complete the Installation by flashing a full OpenWRT image.  Note:
  you may use the sysupgrade command line tool in lieu of the UI if
  you prefer.
  a.  Choose System -> Backup/Flash Firmware.
  b.  Click "Flash Image..." under "Flash new firmware image"
  c.  Click "Browse..." and then select the sysupgrade file.
  d.  Click Upload to upload the sysupgrade file.
  e.  Important:  uncheck "Keep settings and retain the current
      configuration" for this initial installation.
  f.  Click "Continue" to flash the firmware.
  g.  The device will reboot and OpenWRT is installed.

Extender (ALLY-00X19K)
1) This device requires a TFTP recovery procedure to do an initial load
  of OpenWRT.  Start by configuring a computer as a TFTP client:
  a. Install a TFTP client (server not necessary)
  b. Configure an Ethernet interface to 192.168.1.x/24; don't use .1 or .6
  c. Connect the Ethernet to the sole Ethernet port on the X19K.
2) Put the ALLY Extender in TFTP recovery mode.
  a. Do this by pressing and holding the reset button on the bottom while
  connecting the power.
  b. As soon as the LED lights up green (roughly 2-3 seconds), release
  the button.
3) Start the TFTP transfer of the Initramfs image from your setup machine.
For example, from Linux:
tftp -v -m binary 192.168.1.6 69 -c put initramfs.bin
4) The Extender will flash the OpenWrt initramfs image and reboot.  After
booting, LuCI will be available on 192.168.1.1.
5) Log into LuCI as root; there is no password.
6) Optional (but recommended) is to backup the OEM firmware before
  continuing; see process below.
7) Complete the Installation by flashing a full OpenWRT image.  Note: you
may use the sysupgrade command line tool in lieu of the UI if you prefer.
  a.  Choose System -> Backup/Flash Firmware.
  b.  Click "Flash Image..." under "Flash new firmware image"
  c.  Click "Browse..." and then select the sysupgrade file.
  d.  Click Upload to upload the sysupgrade file.
  e.  Important:  uncheck "Keep settings and retain the current
      configuration" for this initial installation.
  f.  Click "Continue" to flash the firmware.
  g.  The device will reboot and OpenWRT is installed.

Backup the OEM Firmware:
-----------------------

There isn't any downloadable firmware for the ALLY devices on the Amped
Wireless web site. Reverting back to the OEM firmware is not possible
unless we have a backup of the original OEM firmware.

The OEM firmware may be stored on either /dev/mtd3 ("firmware") or
/dev/mtd6 ("oem").  We can't be sure which was overwritten with the
initramfs image, so backup both partitions to be safe.

  1) Once logged into LuCI, navigate to System -> Backup/Flash Firmware.
  2) Under "Save mtdblock contents," first select "firmware" and click
  "Save mtdblock" to download the image.
  3) Repeat the process, but select "oem" from the pull-down menu.

Revert to the OEM Firmware:
--------------------------
* U-boot TFTP:
  Follow the TFTP recovery steps for the Extender, and use the
  backup image.

* OpenWrt "Flash Firmware" interface:
  Upload the backup image and select "Force update"
  before continuing.

Signed-off-by: Jonathan Sturges <jsturges@redhat.com>