phy: rcar-gen3-usb2: Add support for r8a77470

This patch adds support for r8a77470 (RZ/G1C). We can reuse this driver for
initializing timing/interrupt generation registers.

Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>