dt-bindings: gpio: rcar: Add r8a77470 (RZ/G1C) support

Renesas RZ/G1C (R8A77470) SoC GPIO blocks are identical to the R-Car Gen2
family. Add support for its GPIO controllers.

Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Reviewed-by: Chris Paterson <chris.paterson2@renesas.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>