dt-bindings: rcar-gen3-phy-usb2: Add r8a774b1 support

Document RZ/G2N (R8A774B1) SoC bindings.
Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/1570531132-21856-2-git-send-email-fabrizio.castro@bp.renesas.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/phy/rcar-gen3-phy-usb2.txt

@@ -10,6 +10,8 @@ Required properties:
 	      SoC.
 	      "renesas,usb2-phy-r8a774a1" if the device is a part of an R8A774A1
 	      SoC.
+	      "renesas,usb2-phy-r8a774b1" if the device is a part of an R8A774B1
+	      SoC.
 	      "renesas,usb2-phy-r8a774c0" if the device is a part of an R8A774C0
 	      SoC.
 	      "renesas,usb2-phy-r8a7795" if the device is a part of an R8A7795