dt-bindings: arm: Document Renesas H2-based Stout DT bindings

Document the Renesas H2 Stout (ADAS Starterkit) device tree bindings,
listing it as a supported board.

This allows to use checkpatch.pl to validate .dts files referring to
the Stout board.
Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

Documentation/devicetree/bindings/arm/shmobile.txt

@@ -116,6 +116,8 @@ Boards:
     compatible = "renesas,sk-rzg1e", "renesas,r8a7745"
   - SK-RZG1M (YR8A77430S000BE)
     compatible = "renesas,sk-rzg1m", "renesas,r8a7743"
+  - Stout (ADAS Starterkit, Y-R-CAR-ADAS-SKH2-BOARD)
+    compatible = "renesas,stout", "renesas,r8a7790"
   - V3MSK
     compatible = "renesas,v3msk", "renesas,r8a77970"
   - Wheat