arm64: renesas: document V3MSK board bindings

Document the V3M Starter Kit device tree bindings, listing it as
a supported board.

This allows to use checkpatch.pl to validate .dts files referring to
the V3MSK board.
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

Documentation/devicetree/bindings/arm/shmobile.txt

@@ -112,6 +112,8 @@ Boards:
     compatible = "renesas,sk-rzg1e", "renesas,r8a7745"
   - SK-RZG1M (YR8A77430S000BE)
     compatible = "renesas,sk-rzg1m", "renesas,r8a7743"
+  - V3MSK
+    compatible = "renesas,v3msk", "renesas,r8a77970"
   - Wheat
     compatible = "renesas,wheat", "renesas,r8a7792"