ramips: add support for Huasifei WS1208V2

ramips: add support for Huasifei WS1208V2

The Huasifei WS1208V2 is an AC1200 router featuring 5 Ethernet ports with a
Quectel RM520N-GL cellular modem which supports QMI and MBIM modes.

Specifications:
- MT7621AT, 256 MiB RAM, 16 MiB SPI Flash
- MT7603EN 2.4 GHz & MT7612EN 5 GHz WLAN
- Quectel RM520N-GL Cellular Modem
- 2 WLAN & 4 Cellular Antennas
- 5 Gigabit Ethernet Ports
- 1 USB 2.0 port
- 1 PCI-E Slot
- 1 M.2 slot
- 1 SIM card slot
- 1 SD card slot

Installation:
- Install sysupgrade image via ROOter OS.

TFTP Recovery:
- Connect to serial console.
- Boot initramfs image by choosing option 1 when U-Boot prompts.
- Install sysupgrade image via OpenWrt.

Link: https://www.huasifei.com/a/Products/5G%20CPE/240.html
Signed-off-by: Arınç ÜNAL <arinc.unal@arinc9.com>