net: ethernet: mtk_wed: introduce wed mcu support

Introduce WED mcu support used to configure WED WO chip.
This is a preliminary patch in order to add RX Wireless
Ethernet Dispatch available on MT7986 SoC.

Tested-by: Daniel Golle <daniel@makrotopia.org>
Co-developed-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Sujuan Chen <sujuan.chen@mediatek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>