usb: rockchip-phy: implement USB2.0 phy control

So far, Rockchip SoCs have two kinds of USB2.0 phy, such as Synopsys and
Innosilicon. This patch applys dwc2 usb driver framework to implement
phy_init() and phy_off() methods for Synopsys phy on Rockchip platform.

Signed-off-by: Ziyuan Xu <xzy.xu@rock-chips.com>
Acked-by: Simon Glass <sjg@chromium.org>