dt-bindings: dma: renesas,usb-dmac: add r8a77961 support

This patch adds support for r8a77961 (R-Car M3-W+).
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/1585117138-8408-1-git-send-email-yoshihiro.shimoda.uh@renesas.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

Documentation/devicetree/bindings/dma/renesas,usb-dmac.txt

@@ -16,6 +16,7 @@ Required Properties:
 	  - "renesas,r8a7794-usb-dmac" (R-Car E2)
 	  - "renesas,r8a7795-usb-dmac" (R-Car H3)
 	  - "renesas,r8a7796-usb-dmac" (R-Car M3-W)
+	  - "renesas,r8a77961-usb-dmac" (R-Car M3-W+)
 	  - "renesas,r8a77965-usb-dmac" (R-Car M3-N)
 	  - "renesas,r8a77990-usb-dmac" (R-Car E3)
 	  - "renesas,r8a77995-usb-dmac" (R-Car D3)