phy: rockchip: Add Rockchip USB2PHY driver

Add Rockchip USB2PHY driver with initial support.

This will help to use it for EHCI controller in host
mode, and USB 3.0 controller in otg mode.

More functionality like charge, vbus detection will
add it in future changes.

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Signed-off-by: Frank Wang <frank.wang@rock-chips.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>