dt-bindings: arm: renesas: Document beacon-rzg2m

Beacon EmbeddedWorks is introducing a development kit based on the
Renesas RZ/G2M platform.  This patch adds the entry to the bindings
list.
Signed-off-by: Adam Ford <aford173@gmail.com>
Link: https://lore.kernel.org/r/20200714123419.3390-2-aford173@gmail.comSigned-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

Documentation/devicetree/bindings/arm/renesas.yaml

@@ -118,6 +118,7 @@ properties:
         items:
           - enum:
               - hoperun,hihope-rzg2m # HopeRun HiHope RZ/G2M platform
+              - beacon,beacon-rzg2m # Beacon EmbeddedWorks RZ/G2M Kit
           - const: renesas,r8a774a1
 
       - items: