ramips: Add support for Ruijie RG-EW1200G PRO v1.1

ramips: Add support for Ruijie RG-EW1200G PRO v1.1

    SoC: MediaTek MT7621
    Flash: 16MB (Macronix MX25L12805D)
    RAM: 128MB
    Serial: As marked on PCB, baudrate is 57600, DO NOT CONNECT 3.3V!!!
    Ethernet: 4x 10/100/1000 Mbps (3x LAN + WAN)
    WIFI0: MT7615 2.4GHz 802.11b/g/n
    WIFI1: MT7615 5GHz 802.11ac
    Antennas: 6x external (3 per radio), non-detachable
    LEDs: Programmable power-LED (blue-colored)
    Buttons: Reset

INSTALLATION:

    Get rootshell using insructions from https://gist.github.com/ZIKH26/18693c67ee7d2f8d2c60231b19194c37

    Download and flash image
    On computer:
    python -m http.server
    On router:
    cd /tmp
    wget http://:8000/factory.bin
    mtd -r write factory.bin firmware

Device should reboot at this point.

Reverting to stock:
Download archive with firmware from Ruijie's site and
get .bin file from it. Then write that binary to firmware
partition. After reboot, factory-reset the router using
reset button.

Signed-off-by: Yahor Leonenka <staryjakau@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/16202
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>