ath79: add support for Senao Engenius EAP350 v1

ath79: add support for Senao Engenius EAP350 v1

FCC ID: U2M-EAP350

Engenius EAP350 is a wireless access point with 1 gigabit PoE ethernet port,
2.4 GHz wireless, external ethernet switch, and 2 internal antennas.

Specification:

  - AR7242 SOC
  - AR9283 WLAN			(2.4 GHz, 2x2, PCIe on-board)
  - AR8035-A switch		(GbE with 802.3af PoE)
  - 40 MHz reference clock
  - 8 MB FLASH			MX25L6406E
  - 32 MB RAM			EM6AA160TSA-5G
  - UART at J2			(populated)
  - 3 LEDs, 1 button		(power, eth, 2.4 GHz) (reset)
  - 2 internal antennas

MAC addresses:

  MAC address is labeled as "MAC"
  Only 1 address on label and in flash
  The OEM software reports these MACs for the ifconfig

  eth0	MAC	*:0c	art 0x0
  phy0	---	*:0d	---

Installation:

  2 ways to flash factory.bin from OEM:

  - if you get Failsafe Mode from failed flash:
      only use it to flash Original firmware from Engenius
      or risk kernel loop or halt which requires serial cable

  Method 1: Firmware upgrade page:

    OEM webpage at 192.168.10.1
    username and password "admin"
    Navigate to "Upgrade Firmware" page from left pane
    Click Browse and select the factory.bin image
    Upload and verify checksum
    Click Continue to confirm and wait 3 minutes

  Method 2: Serial to load Failsafe webpage:

    After connecting to serial console and rebooting...
    Interrupt uboot with any key pressed rapidly
    execute `run failsafe_boot` OR `bootm 0x9f670000`
    wait a minute
    connect to ethernet and navigate to
    "192.168.1.1/index.htm"
    Select the factory.bin image and upload
    wait about 3 minutes

Return to OEM:

  If you have a serial cable, see Serial Failsafe instructions
  otherwise, uboot-env can be used to make uboot load the failsafe image

  *DISCLAIMER*
  The Failsafe image is unique to Engenius boards.
  If the failsafe image is missing or damaged this will not work
  DO NOT downgrade to ar71xx this way, it can cause kernel loop or halt

  ssh into openwrt and run
  `fw_setenv rootfs_checksum 0`
  reboot, wait 3 minutes
  connect to ethernet and navigate to 192.168.1.1/index.htm
  select OEM firmware image from Engenius and click upgrade

Format of OEM firmware image:

  The OEM software of EAP350 is a heavily modified version
  of Openwrt Kamikaze. One of the many modifications
  is to the sysupgrade program. Image verification is performed
  simply by the successful ungzip and untar of the supplied file
  and name check and header verification of the resulting contents.
  To form a factory.bin that is accepted by OEM Openwrt build,
  the kernel and rootfs must have specific names...

    openwrt-senao-eap350-uImage-lzma.bin
    openwrt-senao-eap350-root.squashfs

  and begin with the respective headers (uImage, squashfs).
  Then the files must be tarballed and gzipped.
  The resulting binary is actually a tar.gz file in disguise.
  This can be verified by using binwalk on the OEM firmware images,
  ungzipping then untaring.

  The OEM upgrade script is at /etc/fwupgrade.sh

  Later models in the EAP series likely have a different platform
  and the upgrade and image verification process differs.

  OKLI kernel loader is required because the OEM software
  expects the kernel to be no greater than 1024k
  and the factory.bin upgrade procedure would
  overwrite part of the kernel when writing rootfs.

Note on PLL-data cells:

  The default PLL register values will not work
  because of the external AR8035-A switch between
  the SOC and the ethernet PHY chips.

  For AR724x series, the PLL register for GMAC0
  can be seen in the DTSI as 0x2c.
  Therefore the PLL register can be read from uboot
  for each link speed after attempting tftpboot
  or another network action using that link speed
  with `md 0x1805002c 1`.

  uboot did not have a good value for 1 GBps
  so it was taken from other similar DTS file.

Tested from master, all link speeds functional

Signed-off-by: Michael Pratt <mcpratt@pm.me>