mt76x0: align mt76x0u and mt76x0e fw version

Unify firmware version used on mt76x0e and mt76x0u drivers.
Fallback to mt7610u fw if mt7610e one is not available

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