mediatek-filogic: add support for OpenWRT One (#3446)

Specification:
 - MT7981 CPU using 2.4GHz and 5GHz WiFi (both AX)
 - 1GB RAM
 - 16MB NOR
 - 128MB NAND
 - 3 LEDs (red, green, blue, white)
 - 2 buttons (reset, user defined)
 - 1 2.5Gbit WAN port (Airoha EN8811h)
 - 1 1Gbit LAN ports
 - 1 single lane M.2 SSD slot
 - 1 mikroBus socket
 - externel HW WDT (25s refresh time)
 - i2c RTC (with battery backup)

Serial Interface
 - UBS-C CDC-ACM
 - 3 Pins GND, RX, TX
 - Settings: 115200, 8N1