dt-bindings: gpio: rcar: Add DT binding for r8a774b1

Document Renesas' RZ/G2N (R8A774B1) GPIO blocks compatibility within the
relevant dt-bindings.

Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

Documentation/devicetree/bindings/gpio/renesas,gpio-rcar.txt

@@ -8,6 +8,7 @@ Required Properties:
     - "renesas,gpio-r8a7745": for R8A7745 (RZ/G1E) compatible GPIO controller.
     - "renesas,gpio-r8a77470": for R8A77470 (RZ/G1C) compatible GPIO controller.
     - "renesas,gpio-r8a774a1": for R8A774A1 (RZ/G2M) compatible GPIO controller.
+    - "renesas,gpio-r8a774b1": for R8A774B1 (RZ/G2N) compatible GPIO controller.
     - "renesas,gpio-r8a774c0": for R8A774C0 (RZ/G2E) compatible GPIO controller.
     - "renesas,gpio-r8a7778": for R8A7778 (R-Car M1) compatible GPIO controller.
     - "renesas,gpio-r8a7779": for R8A7779 (R-Car H1) compatible GPIO controller.