wifi: mt76: Add mt76_dma_get_rxdmad_c_buf utility routione

Introduce mt76_dma_get_rxdmad_c_buf routine to process packets received
by HW-RRO v3.1 module.
This is a preliminary patch to introduce SW path for HW-RRO v3.1 module
available on MT7992 chipset.

Co-developed-by: Rex Lu <rex.lu@mediatek.com>
Signed-off-by: Rex Lu <rex.lu@mediatek.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/20250909-mt7996-rro-rework-v5-15-7d66f6eb7795@kernel.org


Signed-off-by: Felix Fietkau <nbd@nbd.name>