mt76x0: use mt76x02 utility routines in mt76x0 init code

Use mt76x02_wait_for_wpdma and mt76x02_wait_for_txrx_idle
utility routines in mt76x0_init_hardware and mt76x0_mac_start
and remove duplicated code

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