usb: phy: add R-Car USB phy driver

This patch adds Renesas R-Car USB phy driver.
It supports R8A7779 chip at this point.

R-Car has some USB controllers, but has only one phy-initializer.
So, this driver is counting users.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>