mt76: move mt76x2_eeprom_get in mt76x02_eeprom.h

Move mt76x2_eeprom_get utility routine in mt76x02_eeprom.h since
it will be used to parse mt76x0 eeprom in order to unify eeprom
support between mt76x2 and mt76x0 drivers

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