soc: renesas: rcar-rst: add R8A77970 support

Add support for R-Car V3M (R8A77970) to the R-Car RST driver -- this driver
is  needed  for the clock driver to work.

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

Documentation/devicetree/bindings/reset/renesas,rst.txt

@@ -26,6 +26,7 @@ Required properties:
 		  - "renesas,r8a7794-rst" (R-Car E2)
 		  - "renesas,r8a7795-rst" (R-Car H3)
 		  - "renesas,r8a7796-rst" (R-Car M3-W)
+		  - "renesas,r8a77970-rst" (R-Car V3M)
 		  - "renesas,r8a77995-rst" (R-Car D3)
   - reg: Address start and address range for the device.