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

Document RZ/G2E (R8A774C0) SoC bindings.

Signed-off-by: Fabrizio Castro <[e-mail]>
Reviewed-by: Yoshihiro Shimoda <[e-mail]>
Reviewed-by: Simon Horman <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Signed-off-by: Kishon Vijay Abraham I <[e-mail]>

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

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 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.
 	      "renesas,usb2-phy-r8a7796" if the device is a part of an R8A7796