net: ethernet: mtk_eth_soc: introduce flow offloading support for mt7986

Introduce hw flow offload support for mt7986 chipset. PPE is not enabled
yet in mt7986 since mt76 support is not available yet.

Tested-by: Daniel Golle <daniel@makrotopia.org>
Co-developed-by: Bo Jiao <Bo.Jiao@mediatek.com>
Signed-off-by: Bo Jiao <Bo.Jiao@mediatek.com>
Co-developed-by: Sujuan Chen <sujuan.chen@mediatek.com>
Signed-off-by: Sujuan Chen <sujuan.chen@mediatek.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>