pinctrl/rockchip: add pinctrl device to gpio bank struct

Store a pointer from the pinctrl device for the gpio bank.

Signed-off-by: Jianqun Xu <jay.xu@rock-chips.com>
Link: https://lore.kernel.org/r/20210816011948.1118959-4-jay.xu@rock-chips.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>