mediatek: add Huasifei WH3000R NAND support

mediatek: add Huasifei WH3000R NAND support

**Huasifei WH3000R NAND**
Wi-Fi 6 router based on MediaTek MT7981B SoC.
MT7981B+MT7976CN+MT7531AE

**Specifications**
SoC: Filogic 820 MT7981B (1.3GHz)
RAM: DDR3 512MB
Flash: 256MiB Winbond SPI NAND
WiFi: MT7976C: 2.4GHz 2x2, 5GHz 2x2
Ethernet: MT7531: 3x 1GbE LAN + 1x 1GbE WAN
USB: 1x USB 3.0 port
Two buttons: reset and mesh
LEDs: RGB (red, green, blue together)
UART: 3.3V, TX, RX, GND / 115200 8N1
DC power interface

+---------+-------------------+--------------------------+
|         | MAC               | Algorithm                |
+---------+-------------------+--------------------------+
| LAN     | 58:23:BC:xx:xx:x2 | label+1                  |
| WAN     | 58:23:BC:xx:xx:x1 | label+0 (eeprom)         |
| WLAN 2g | 58:23:BC:xx:xx:x3 | label+2                  |
| WLAN 5g | 58:23:BC:xx:xx:x4 | label+3                  |
+---------+-------------------+--------------------------+
Since it's convenient for the users to check and tell MAC
to their internet providers from the router label, we set
WAN as a base MAC located at 'Factory', 0x4.
Discussed this with the vendor.

**Installation via U-Boot rescue**
1. Set static IP 192.168.1.2 on your computer and default route as 192.168.1.1
2. Connect to the LAN port and hold the reset button while booting the device.
3. Wait for the LED to blink 5 times, and release the reset button.
4. Open U-boot web page on your browser at http://192.168.1.1
5. Select the OpenWrt sysupgrade image, upload it, and start the upgrade.
6. Wait for the router to flash the new firmware.
7. Wait for the router to reboot itself.

**Installation via sysupgrade**
Just flash sysupgrade file via
[LuCI upgrade page](http://192.168.1.1/cgi-bin/luci/admin/system/flash)
without saving the settings.

**Installation via SSH**
Upload the file to the router `/tmp` directory, `ssh root@192.168.1.1`
and issue a command:
```
sysupgrade -n /tmp/openwrt-mediatek-filogic-huasifei_wh3000r-nand-squashfs-sysupgrade.bin
```

Signed-off-by: Fil Dunsky <filipp.dunsky@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/23156
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>