gpio: rcar: Add r8a77995 (R-Car D3) support

This patch adds binding for r8a77995 (R-Car D3). This SoC can use
"renesas,rcar-gen3-gpio" fallback compatibility. So, this patch
doesn't modify the gpio-rcar driver.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Acked-by: Simon Horman <horms+renesas@verge.net.au>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>