mt76: move mt76x02_set_tx_ackto in mt76x02-lib module

Move mt76x02_set_tx_ackto and mt76x02_set_coverage_class routines
in mt76x02-lib module in order to be reused by mt76x0 driver.
This is a preliminary patch to unify drv_bss_info_changed mac80211
callback between mt76x0 and mt76x2 drivers

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