gpio: loongson: add gpio driver support

The Loongson platforms GPIO controller contains 60 GPIO pins in total,
4 of which are dedicated GPIO pins, and the remaining 56 are reused
with other functions. Each GPIO can set input/output and has the
interrupt capability.

This driver added support for Loongson GPIO controller and support to
use DTS or ACPI to descibe GPIO device resources.

Signed-off-by: Jianmin Lv <lvjianmin@loongson.cn>
Signed-off-by: Hongchen Zhang <zhanghongchen@loongson.cn>
Signed-off-by: Liu Peibao <liupeibao@loongson.cn>
Signed-off-by: Juxin Gao <gaojuxin@loongson.cn>
Signed-off-by: Yinbo Zhu <zhuyinbo@loongson.cn>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>