arm64: dts: mediatek: mt7622: add support for coherent DMA

[ Upstream commit 3abd0630 ]

It improves performance by eliminating the need for a cache flush on rx and tx

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: 3ba5a615 ("arm64: dts: mediatek: mt7622: fix clock controllers")
Signed-off-by: Sasha Levin <sashal@kernel.org>