phy: socionext: add USB2 PHY driver for UniPhier SoC

Add a driver for PHY interface built into USB2 controller implemented on
UniPhier SoCs. This driver supports HS-PHY for Pro4 and LD11.

Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>