ramips: add support for Keenetic Lite III rev. A

ramips: add support for Keenetic Lite III rev. A

General specification:
SoC Type: MediaTek MT7620N (580MHz)
ROM: 8 MB SPI-NOR (W25Q64FV)
RAM: 64 MB DDR (EM6AB160TSD-5G)
Switch: MediaTek MT7530
Ethernet: 5 ports - 5×100MbE (WAN, LAN1-4)
Wireless: 2.4 GHz (MediaTek RT5390): b/g/n
Buttons: 3 button (POWER, RESET, WPS)
Slide switch: 4 position (BASE, ADAPTER, BOOSTER, ACCESS POINT)
Bootloader: U-Boot 1.1.3
Power: 9 VDC, 0.6 A

MAC in stock:
|-	+			|
| LAN 	| RF-EEPROM + 0x04	|
| WLAN	| RF-EEPROM + 0x04	|
| WAN 	| RF-EEPROM + 0x28	|

OEM easy installation
1. Use a PC to browse to http://my.keenetic.net.
2. Go to the System section and open the Files tab.
3. Under the Files tab, there will be a list of system
files. Click on the Firmware file.
4. When a modal window appears, click on the Choose File
button and upload the firmware image.
5. Wait for the router to flash and reboot.

OEM installation using the TFTP method
1. Download the latest firmware image and rename it to
klite3_recovery.bin.
2. Set up a Tftp server on a PC (e.g. Tftpd32) and place the
firmware image to the root directory of the server.
3. Power off the router and use a twisted pair cable to connect
the PC to any of the router's LAN ports.
4. Configure the network adapter of the PC to use IP address
192.168.1.2 and subnet mask 255.255.255.0.
5. Power up the router while holding the reset button pressed.
6. Wait approximately for 5 seconds and then release the
reset button.
7. The router should download the firmware via TFTP and
complete flashing in a few minutes.
After flashing is complete, use the PC to browse to
http://192.168.1.1 or ssh to proceed with the configuration.

Signed-off-by: Alexey Bartenev <41exey@proton.me>
(cherry picked from commit dc79b51533cfe9a7806353f6c6fd6b22cd80d536)