arm: dts: mt2701: Add usb3 device nodes

Add xhci nodes and usb3 phy nodes for MT2701

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Signed-off-by: Erin Lo <erin.lo@mediatek.com>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>