net: ethernet: mtk_eth_soc: introduce MTK_NETSYS_V2 support

Introduce MTK_NETSYS_V2 support. MTK_NETSYS_V2 defines 32B TX/RX DMA
descriptors.
This is a preliminary patch to add mt7986 ethernet support.

Tested-by: Sam Shih <[email protected]>
Signed-off-by: Lorenzo Bianconi <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: LorenzoBianconi