dt-bindings: gpio: renesas,rcar-gpio: Add r8a779g0 support

Document support for the GPIO controller blocks in the Renesas R-Car
V4H (R8A779G0) SoC.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>