add a DT binding documentation of usb3.0 phy for MT65xx
SoCs from Mediatek.
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NChunfeng Yun <chunfeng.yun@mediatek.com>
Signed-off-by: NKishon Vijay Abraham I <kishon@ti.com>