phy: socionext: add USB3 PHY driver for UniPhier SoC

Add a driver for PHY interface built into USB3 controller
implemented in UniPhier SoCs.
This driver supports High-Speed PHY and Super-Speed PHY.

Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Signed-off-by: Motoya Tanigawa <tanigawa.motoya@socionext.com>
Signed-off-by: Masami Hiramatsu <masami.hiramatsu@linaro.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>