dmaengine: rcar-dmac: document R8A77970 bindings

Renesas R-Car V3M (R8A77970) SoC also has the R-Car gen2/3 compatible DMA
controllers, so document the SoC specific binding.
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Acked-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

@@ -25,6 +25,7 @@ Required Properties:
 		- "renesas,dmac-r8a7794" (R-Car E2)
 		- "renesas,dmac-r8a7795" (R-Car H3)
 		- "renesas,dmac-r8a7796" (R-Car M3-W)
+		- "renesas,dmac-r8a77970" (R-Car V3M)
 
 - reg: base address and length of the registers block for the DMAC