dmaengine: rcar-dmac: Document R-Car M3-W bindings

Signed-off-by: Ulrich Hecht <ulrich.hecht+renesas@gmail.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

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

@@ -24,6 +24,7 @@ Required Properties:
 		- "renesas,dmac-r8a7793" (R-Car M2-N)
 		- "renesas,dmac-r8a7794" (R-Car E2)
 		- "renesas,dmac-r8a7795" (R-Car H3)
+		- "renesas,dmac-r8a7796" (R-Car M3-W)
 
 - reg: base address and length of the registers block for the DMAC