usb: renesas_usbhs: add R-Car Gen3 power control

Since the usb2 phy driver for gen3 (phy-rcar-gen3-usb2) cannot access
LPSTS and UGCTRL2 registers in the HSUSB module, this driver have to
initialize the registers. So, this patch adds such handling code into
rcar3.c.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>