ramips: add support for TOTOLINK A3

ramips: add support for TOTOLINK A3

TOTOLINK A3 is a clone of ipTIME A3. The only difference is the model name.

Specifications:
- SoC: MT7628AN
- RAM: DDR2 64MB
- Flash: SPI NOR 8MB
- WiFi:
  - 2.4GHz: SoC internal
  - 5GHz: MT7612EN
- Ethernet: 3x 10/100Mbps
  - Switch: SoC internal

Installation via web interface:
1.  Flash **initramfs** image through the stock web interface.
2.  Boot into OpenWrt and perform sysupgrade with sysupgrade image.

Revert to stock firmware:
1.  Perform sysupgrade with stock image.

Tested on device by JasonHCH <hsuan670629@gmail.com>

Signed-off-by: Sungbo Eo <mans0n@gorani.run>