gpio: hisi: Add initial device tree support

Add support for HiSilicon GPIO controller in embedded platform, which
boot from devicetree.

Signed-off-by: Weilong Chen <chenweilong@huawei.com>
Acked-by: Jay Fang <f.fangjian@huawei.com>
Reviewed-by: Yicong Yang <yangyicong@hisilicon.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>