mediatek: filogic: add support for WAVLINK WL-WN573HX3

mediatek: filogic: add support for WAVLINK WL-WN573HX3

The WL-WN573HX3 is an AX3000 outdoor Access Point by WAVLINK,
also sold in Europe as 7Links WLR-1300 (ZX-5612).

Specifications:

- MT7981B + MT7976 AX3000 2x2 DBDC (160 MHz)
- 16 MiB SPI NOR, 256 MiB RAM
- Gigabit ethernet port, 802.3af PoE
- IP67 outdoor case for wall or pole mounting with
    four single band RP-SMA fiberglass antennas (8 dBi)

Installation:

- OEM Web UI is at 192.168.30.1 which will forward to
    http://netlogin.link (using a captive portal)
- login with default password `admin`
- skip setup wizard by navigating directly to
    http://netlogin.link/html/meshUpgrade.html
- upload WN573HX3-sysupgrade.bin
- reset to factory defaults to discard OEM UCI settings

MAC address assignment:

LAN         80:xx:xx:76:xx:25  hw 0x44e
WLAN 2.4G   80:xx:xx:76:xx:27  factory 0x04 (label MAC)
WLAN 5G	    82:xx:xx:46:xx:27
pair key    8a:xx:xx:76:xx:27  also on label, not used by OpenWrt

Signed-off-by: Sebastian Schaper <openwrt@sebastianschaper.net>