net: ethernet: mediatek: Integrate hardware path from GMAC to PHY variants

All path route on various SoCs all would be managed in common function
mtk_setup_hw_path that is determined by the both applied devicetree
regarding the path between GMAC and the target PHY or switch by the
capability of target SoC in the runtime.

Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>