mediatek: add support for Hiveton H5000M

mediatek: add support for Hiveton H5000M

Hardware specification:
SoC: MediaTek MT7987A
Flash: 8GB eMMC
RAM: 1GB DDR4
Ethernet: 2x 2.5GbE (RTL8221B PHY + Internal PHY)
WiFi: MediaTek MT7992 / 2+3 antenna variant
Interface: M.2 USB for 5G module
LED: Power (hw-controlled), 2.5G WAN (user-definable),
5G Module (hw-controlled), LED-3 (user-definable),
LED-4 (user-definable)
Button: Reset, WPS
Power: USB Type-C PD
Other: PWM Fan control

MAC address assignment is unconventional: the board has no Factory
partition with pre-programmed MACs. Instead, all addresses are
derived from the eMMC CID at runtime:

  LAN : macaddr_generate_from_mmc_cid mmcblk0
  WAN : LAN + 1 (label_mac)
  phy0: LAN + 2
  phy1: LAN + 3

This matches the vendor firmware behaviour and ensures stable,
unique addresses across reboots without a dedicated EEPROM region
for MACs.

Flash instructions:

Factory `mmcblk0p2` partition is empty,
stock ImmortalWrt-798x-mt799x-6.6-mtwifi from PadavanOnly firmware
uses `MT7991_MT7976_EEPROM_BE5040_iPAiLNA.bin`.
Flashing this eeprom before flashing OpenWrt will make OpenWrt read eeprom:
```
dd if=/lib/firmware/MT7991_MT7976_EEPROM_BE5040_iPAiLNA.bin of=/dev/mmcblk0p2 bs=1 count=7680
sync
```
But it will have wifi issues for now. It's better to use OpenWrt fallback eeprom for now.

Power off the device.
Press and hold the Reset button.
Power on the device while keeping the Reset button pressed.
Wait for the device to enter U-Boot recovery mode.
Connect to the device via Ethernet (default IP: 192.168.1.1).
Set your PC's IP to 192.168.1.x (e.g., 192.168.1.100).
Open a web browser and navigate to http://192.168.1.1
Upload and flash the OpenWrt firmware
Wait for the flashing process to complete and the device to reboot.

Signed-off-by: Fil Dunsky <filipp.dunsky@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/21398
Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>