ramips: Fix wmac dts definition for TP-Link TL-MR6400 v4 and v5

ramips: Fix wmac dts definition for TP-Link TL-MR6400 v4 and v5

This code assumed that the mt7628an_tplink_8m.dtsi file defines
mediatek,mtd-eeprom for the wmac and sets status to okay.

The mediatek,mtd-eeprom definition was removed in commit e93f41adee3e
("ramips: convert MT7628 EEPROM to NVMEM format") but the dts for these
two devices was not adapted to include the eeprom position on its own.

The status = "okay" property was removed in 0a1d15642fa6 ("ramips:
mt7628: use nvmem-layout"), but the property was not added to these dts
files.

Without this change wifi does not work for these devices.

Fixes: e93f41adee3e ("ramips: convert MT7628 EEPROM to NVMEM format")
Fixes: 0a1d15642fa6 ("ramips: mt7628: use nvmem-layout")
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>