dt-bindings: usb: usb-xhci: add r8a77961 support

This patch adds support for r8a77961 (R-Car M3-W+).

To avoid confusion between R-Car M3-W (R8A77960) and R-Car M3-W+
(R8A77961), this patch also updates the comment of
"renesas,xhci-r8a7796".
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Felipe Balbi <balbi@kernel.org>

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

@@ -16,7 +16,8 @@ Required properties:
     - "renesas,xhci-r8a7791" for r8a7791 SoC
     - "renesas,xhci-r8a7793" for r8a7793 SoC
     - "renesas,xhci-r8a7795" for r8a7795 SoC
-    - "renesas,xhci-r8a7796" for r8a7796 SoC
+    - "renesas,xhci-r8a7796" for r8a77960 SoC
+    - "renesas,xhci-r8a77961" for r8a77961 SoC
     - "renesas,xhci-r8a77965" for r8a77965 SoC
     - "renesas,xhci-r8a77990" for r8a77990 SoC
     - "renesas,rcar-gen2-xhci" for a generic R-Car Gen2 or RZ/G1 compatible