ramips: add support for UniElec U7628-01

ramips: add support for UniElec U7628-01

UniElec U7628-01 is a router platform board based on MediaTek MT7628AN.
The device has the following specifications:

- MT7628AN (580MHz)
- 64/128/256 MB of RAM (DDR2)
- 8/16 MB of flash (SPI NOR)
- 5x 10/100 Mbps Ethernet (MT7628 built-in switch)
- 1x 2T2R 2.4 GHz Wi-Fi (MT7628)
- 1x miniPCIe slot (with PCIe and USB 2.0 buses)
- 1x miniSIM slot
- 1x microSD slot
- 1x USB 2.0 port
- 7x single-color LEDs (GPIO-controlled)
- 1x bi-color LED (green GPIO-controlled, red -> LED_WLAN# in miniPCIe)
- 1x reset button
- 1x UART header (4-pins)
- 1x SDXC/GPIO header (10-pins, connected with microSD slot)
- 1x DC jack for main power (12 V)

The following has been tested and is working:

- Ethernet switch
- miniPCIe slot (tested with modem and Wi-Fi card)
- miniSIM slot
- sysupgrade
- reset button
- USB 2.0 port*

Due to a missing driver (MMC over GPIO) this is not supported:

- microSD card reader

* Warning:
USB buses in miniPCIe and regular A-type socket are connected together,
without any proper analog switch or USB HUB.

Installation:

This board might come with a different firmware versions (MediaTek SDK,
PandoraBox, Padavan, etc.). If your board comes with PandoraBox, you can
install LEDE using sysupgrade. Just SSH to the router and perform forced
sysupgrade (due to a board name mismatch). The default IP of this board
should be: 192.168.1.1 and username/password: root/admin. In case of a
different firmware, you can use web based recovery described below.

Use the following command to perform the sysupgrade (for the 128MB
RAM/16MB flash version):

sysupgrade -n -F lede-ramips-mt76x8-u7628-01-128M-16M-squashfs-sysupgrade.bin

Recovery:

This board contains a Chinese, closed-source bootloader called Breed
(Boot and Recovery Environment for Embedded Devices). Breed supports web
recovery and to enter it, you keep the reset button pressed for around
5 seconds during boot. Your machine will be assigned an IP through DHCP
and the router will use IP address 192.168.1.1. The recovery website is
in Chinese, but is easy to use. Click on the second item in the list to
access the recovery page, then the second item on the next page is where
you select the firmware. In order to start the recovery, you click the
button at the bottom.

SDXC/GPIO header (J3):

 1. SDXC_D3  / I2C_SCLK
 2. SDXC_D2  / I2C_SD
 3. SDXC_D1  / I2S_DI
 4. SDXC_D0  / I2S_WS
 5. SDXC_CMD / I2S_CLK
 6. SDXC_CLK / GPIO0
 7. SDXC_CD  / UART_RXD1
 8. UART_TXD1
 9. 3V3
10. GND

Other notes:

1. The board is available with different amounts of RAM and flash. We
have only added support for the 128/16 MB configuration, as that seems
to be the default. However, all the required infrastructure is in place
for making support for the other configurations easy.

Signed-off-by: Piotr Dymacz <pepe2k@gmail.com>
Signed-off-by: Kristian Evensen <kristian.evensen@gmail.com>