wifi: mt76: mt792x: move more dma shared code in mt792x_dma

Rely on irq_map support, move more dma shared code between mt7921 and
mt7925 in mt792x_dma.c
Move the following dma code in mt792x-lib
- mt792x_dma_enable
- mt792x_dma_reset
- mt792x_wpdma_reset
- mt792x_wpdma_reinit_cond

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Deren Wu <deren.wu@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>