gpio: rcar: Add GPIO hole support

GPIO hole is present in RZ/G1C SoC. Valid GPIO pins on bank3 are in the
range GP3_0 to GP3_16 and GP3_27 to GP3_29. The GPIO pins between GP3_17
to GP3_26 are unused. Add support for handling unused GPIO's.

Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>