ramips: add support for LB-Link BL-W1200

ramips: add support for LB-Link BL-W1200

The BL-W1200 Wireless Router is based on the MT7620A SoC.

Specification:

- MediaTek MT7620A (580 Mhz)
- 64 MB of RAM
- 8 MB of FLASH
- 1x 802.11bgn radio
- 1x 802.11ac radio (MT7612E)
- 5x 10/100/1000 Mbps Ethernet (MT7530)
- 2x external, non-detachable antennas (Wifi 2.4G/5G)
- 1x USB 2.0
- UART (R2) on PCB (57600 8n1)
- 9x LED (1 GPIO controlled), 1x button
- u-Boot bootloader

Known issues:
- No status LED. Used WPS LED during boot/failsafe/sysupgrade.

Installation:
1. Apply initramfs image via factory web-gui.
2. Install sysupgrade image.

How to revert to OEM firmware:
- sysupgrade -n -F stock_firmware.bin

Reviewed-by: Sungbo Eo <mans0n@gorani.run>
Signed-off-by: Pawel Dembicki <paweldembicki@gmail.com>