gpio/rockchip: add driver for rockchip gpio

This patch add support for rockchip gpio controller, which is supported
in pinctrl driver in the past.

With this patch, the pinctrl-rockchip driver will drop gpio related
codes and populate platform driver to gpio-rockchip.

Signed-off-by: Jianqun Xu <jay.xu@rock-chips.com>
Link: https://lore.kernel.org/r/20210816012053.1119069-1-jay.xu@rock-chips.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>