mediatek: filogic: add support for Widelantech WAP430X

mediatek: filogic: add support for Widelantech WAP430X

This AX3000 flying saucer-shaped device is sold under a few names:
- Widelantech WAP430X
  http://www.widelantech.com/?m=home&c=View&a=index&aid=131
- Felicomm
- UeeVii UAP200 (sold on amazon.com)
True name, as marked on the PCB and as appears in the DTS, is WAP430X.

Hardware:
- SoC: Mediatek MT7981B
- RAM: 256MiB DDR3
- ROM: 16MiB NOR flash (Winbond 25Q128JVSQ)
- Wired: one GbE RJ45 port
- Wireless: Mediatek MT7976CN DBDC
- Antennas: Internal (two 2.4 GHz 4.5 dBi, three 5 GHz 6 dBi)
- GPIO: two blue LEDs (status, WLAN), one button (reset)
- Power: DC5521 (12V) or 802.3af PoE (48V 0.3A)
- UART: J500 on PCB [3v3] (Rx) (Tx) (Gnd), 115200n

Original firmware is GECOOS 8.0_2024081000, a fork of OpenWrt 21.02
created by Widelantech. All ports are closed except 443 (web management
interface) and 80 (redirects to 443). UART is locked down, but U-Boot
bootloader is friendly.

Installation is done via UART (see note below).

Method 1: press any key during boot to enter MTK U-Boot bootloader,
then choose option 2 (Upgrade firmware) and upload sysupgrade binary
via TFTP (or via Xmodem).

Method 2: put sysupgrade binary on a webserver (http, not https); after
GECOOS loads, choose option 4 (固件在线升级 = online firmware upgrade)
in the menu and enter the URL to the sysupgrade binary.

Note: GECOOS has a slick web management, and firmware can be uploaded
at https://6.6.6.6/#/system/sysupgrade but it's still not clear how to
convert the sysupgrade binary to a factory binary accepted by the web
interface (WIP).

Signed-off-by: Rani Hod <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/20402
Signed-off-by: Hauke Mehrtens <[email protected]>