Move mt7921_dma_init routine in pci.c and make it static since it is run
just in mt7921_pci_probe(). Get rid of dma.c.
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>