dt-bindings: arm: renesas: Document RZ/G2N SoC DT bindings

Add device tree bindings documentation for the Renesas RZ/G2N (r8a774b1)
SoC.

Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Link: https://lore.kernel.org/r/1567675844-19247-2-git-send-email-biju.das@bp.renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

Documentation/devicetree/bindings/arm/renesas.yaml

@@ -116,6 +116,10 @@ properties:
           - const: hoperun,hihope-rzg2m
           - const: renesas,r8a774a1
 
+      - description: RZ/G2N (R8A774B1)
+        items:
+          - const: renesas,r8a774b1
+
       - description: RZ/G2E (R8A774C0)
         items:
           - enum: