ramips: improve support for WeVO 11AC NAS and W2914NS v2

ramips: improve support for WeVO 11AC NAS and W2914NS v2

- remove WAN port index
- load WAN MAC address directly from the flash
- provide label MAC address
- increase flash's SPI frequency to 80MHz
- add mt76 led nodes to make WiFi LEDs work
- drop unnecessary pinmux groups

The factory partition scheme for MAC addresses (verified on both devices):
0x4   : WiFi 2.4GHz (label_mac-9)
0x28  : unused
0x2e  : WAN (label_mac)
0x8004: WiFi 5GHz (label_mac-5)
0xe000: LAN (label_mac-1)
0xe006: unused

By improving flash speed,
`time dd if=/dev/mtdblock3 of=/dev/null bs=64k`
has been reduced from 14.51s to 3.11s.

Signed-off-by: Sungbo Eo <mans0n@gorani.run>
[rebased]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>