phy: phy-mt65xx-usb3: move clock from phy node into port nodes

each port has its own reference clock, the HighSpeed port is 48M,
and the SuperSpeed port is usually 26M, put them into port node for
flexibility, this can close clock if the port is not used.

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>