wifi: mt76: mt7921: add MT7902e DMA layout support

wifi: mt76: mt7921: add MT7902e DMA layout support

Add MT7902 PCIe specific DMA layout overrides for MCU TXQ index, RX ring
size, and MCU_WA usage. Common layout remains the default for other chips.

This is a prerequisite patch before enabling MT7902 PCIe support.

Co-developed-by: Xiong Huang <xiong.huang@mediatek.com>
Signed-off-by: Xiong Huang <xiong.huang@mediatek.com>
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Link: https://patch.msgid.link/20260219004007.19733-4-sean.wang@kernel.org
Signed-off-by: Felix Fietkau <nbd@nbd.name>