pinctrl: rockchip: add input schmitt support for rv1108

Some pins like i2c SCL/SDA need the schmitt input function
to avoid crosstalk problems.

Signed-off-by: Andy Yan <andy.yan@rock-chips.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>