dt-bindings: rcar-gen3-phy-usb2: Add r8a774c0 support

Document RZ/G2E (R8A774C0) SoC bindings.
Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>

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

@@ -5,6 +5,8 @@ This file provides information on what the device node for the R-Car generation
 
 Required properties:
 - compatible: "renesas,usb2-phy-r8a774a1" if the device is a part of an R8A774A1
+	      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
 	      SoC.