net: ethernet: mtk_wed: introduce WED support for MT7988

Similar to MT7986 and MT7622, enable Wireless Ethernet Ditpatcher for
MT7988 in order to offload traffic forwarded from LAN/WLAN to WLAN/LAN

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: Paolo Abeni <pabeni@redhat.com>