dt-bindings: gpio: rcar: Add r8a779a0 support

Document the compatible value for the GPIO block in the Renesas R-Car
V3U (R8A779A0) SoC.

While this GPIO block is mostly compatible with GPIO blocks on R-Car
Gen3 SoCs, there are small differences, and one of the new registers
needs to be configured differently from its initial reset state.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

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

@@ -48,6 +48,9 @@ properties:
               - renesas,gpio-r8a77995     # R-Car D3
           - const: renesas,rcar-gen3-gpio # R-Car Gen3 or RZ/G2
 
+      - items:
+          - const: renesas,gpio-r8a779a0  # R-Car V3U
+
   reg:
     maxItems: 1