pinctrl: rockchip: Implement .request() and .free() callbacks

Implement .request() and .free() callbacks on the GPIO chips to
inform pinctrl when a GPIO is requested or freed.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Acked-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>