pinctrl/rockchip: drop the gpio related codes

With the patch to separate the gpio driver from the pinctrl driver, now
the pinctrl-rockchip can drop the gpio related codes now.

Signed-off-by: Jianqun Xu <jay.xu@rock-chips.com>
Link: https://lore.kernel.org/r/20210816012146.1119289-1-jay.xu@rock-chips.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>