arm: dts: visconti: Add DT support for Toshiba Visconti5 GPIO driver

Add the GPIO node in Toshiba Visconti5 SoC-specific DT file.
And enable the GPIO node in TMPV7708 RM main board's board-specific DT file.

Signed-off-by: Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@toshiba.co.jp>
Reviewed-by: Punit Agrawal <punit1.agrawal@toshiba.co.jp>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>