mt76: move wait_for_wpdma in mt76x02_dma.h

Move wait_for_wpdma utility routine in mt76x02_dma.h
in order to be reused by mt76x0 driver. Moreover add
the possibility to specify the timeout value in
wait_for_wpdma signature

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