pinctrl: rockchip: Don't call pinctrl_gpio_direction_output() in pin_config_set()

The Rockchip pinctrl driver was calling
rockchip_gpio_direction_output() in the pin_config_set() callback.
This was just a shortcut for:
* rockchip_gpio_set()
* pinctrl_gpio_direction_output()

Unfortunately it's not so good to call pinctrl_gpio_direction_output()
from pin_config_set().  Specifically when initting hogs you'll get an
error.

Let's refactor a little so we can call
_rockchip_pmx_gpio_set_direction() directly.

Signed-off-by: Doug Anderson <dianders@chromium.org>
Tested-by: Chris Zhong <zyw@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>