ath79: add support for COMFAST CF-E120A v3

ath79: add support for COMFAST CF-E120A v3

This patch adds support for the COMFAST CF-E120A v3, an outdoor wireless
CPE with two Ethernet ports and a 802.11an radio.

Specifications:

 - AR9344 SoC
 - 535/400/267 MHz (CPU/DDR/AHB)
 - 2x 10/100 Mbps Ethernet, both with PoE-in support
 - 64 MB of RAM (DDR2)
 - 8 MB of FLASH
 - 2T2R 5 GHz, up to 25 dBm
 - 11 dBi built-in antenna
 - POWER/LAN/WAN/WLAN green LEDs
 - 4x RSSI LEDs (2x red, 2x green)
 - UART (115200 8N1) and GPIO (J9) headers on PCB

Flashing instructions:

 The original firmware is based on OpenWrt so a sysupgrade image can be
 installed via the stock web GUI. Settings from the original firmware
 will be saved and restored on the new one, so a factory reset will be
 needed. To do so, once the new firmware is flashed, enter into failsafe
 mode by pressing the reset button several times during the boot
 process, while while the WAN LED flashes, until it starts flashing
 faster. Once in failsafe mode, perform a factory reset as usual.

 The U-boot bootloader contains a recovery HTTP server to upload the
 firmware. Push the reset button while powering the device on and
 keep it pressed for >10 seconds. The recovery page will be at
 http://192.168.1.1

Signed-off-by: Roger Pueyo Centelles <roger.pueyo@guifi.net>