mediatek: add support for Keenetic/Netcraze (K/N)AP-630

mediatek: add support for Keenetic/Netcraze (K/N)AP-630

This commit adds support for Keenetic/Netcraze (K/N)AP-630

Specification:
 - MT7981 CPU using 2.4GHz and 5GHz WiFi (both AX)
 - 512MB RAM
 - 128MB SPI NAND
 - 1 led with two colors (green, orange)
 - 1 button (reset)
 - 1 2.5Gbit POE ethernet port based on Airoha EN8811H phy

Serial Interface:
 - 3 Pins GND, RX, TX
 - Settings: 115200, 8N1

Notes:
 - The device supports dual boot mode

Flash instruction:
The only way to flash OpenWrt image is to use tftp recovery mode in U-Boot:

1. Configure PC with static IP 192.168.1.2/24 and tftp server.
2. Copy image to tftp server.
 a) Keenetic
    Rename "openwrt-mediatek-filogic-keenetic_kap-630-squashfs-factory.bin"
    to "KAP-630_recovery.bin" and place it in tftp server directory.
 b) Netcraze
    Rename "openwrt-mediatek-filogic-netcraze_nap-630-squashfs-factory.bin"
    to "NAP-630_recovery.bin" and place it in tftp server directory.
3. Connect PC with ethernet port, press the reset button, power up
   the device and keep button pressed until status led start blinking.
4. Device will download file from server, write it to flash and reboot.

Signed-off-by: Maxim Anisimov <maxim.anisimov.ua@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/21634
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>