mt76: move mt76x02_mac_setaddr in mt76x02-lib module

Move mt76x02_mac_setaddr utility routine in mt76x02-lib
module and remove duplicated code. This is a preliminary patch
to unify eeprom code between mt76x2 and mt76x0 driver

Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>