dt-bindings: usb-xhci: Add r8a774a1 support

Document RZ/G2M (R8A774A1) SoC bindings.
Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Biju Das <biju.das@bp.renesas.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/usb/usb-xhci.txt

@@ -8,6 +8,7 @@ Required properties:
     - "marvell,armada-375-xhci" for Armada 375 SoCs
     - "marvell,armada-380-xhci" for Armada 38x SoCs
     - "renesas,xhci-r8a7743" for r8a7743 SoC
+    - "renesas,xhci-r8a774a1" for r8a774a1 SoC
     - "renesas,xhci-r8a7790" for r8a7790 SoC
     - "renesas,xhci-r8a7791" for r8a7791 SoC
     - "renesas,xhci-r8a7793" for r8a7793 SoC
@@ -17,7 +18,8 @@ Required properties:
     - "renesas,xhci-r8a77990" for r8a77990 SoC
     - "renesas,rcar-gen2-xhci" for a generic R-Car Gen2 or RZ/G1 compatible
       device
-    - "renesas,rcar-gen3-xhci" for a generic R-Car Gen3 compatible device
+    - "renesas,rcar-gen3-xhci" for a generic R-Car Gen3 or RZ/G2 compatible
+      device
     - "xhci-platform" (deprecated)
 
     When compatible with the generic version, nodes must list the