pinctrl: rockchip: add support the get_direction

This patch adds the get_direction to support the gpio
interface.

The gpio direction is not used on rockchip platform when use the gpio
debugfs.

Tested on kylin board. (RK3036 SoCs)
The repro steps:
$/sys/class/gpio/
echo 53 > export
$/sys/class/gpio/gpio53# cat direction
in
In general, the gpio53 should be out value, but the direction is the
default value 'in',  since the get_direction didn't supported in rockchip
pinctrl.

So, we should add this patch to support it.

Cc: linux-gpio@vger.kernel.org
Cc: linux-rockchip@lists.infradead.org
Reported-by: Jeffy Chen <jeffy.chen@rock-chips.com>
Signed-off-by: Caesar Wang <wxt@rock-chips.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>