MAINTAINERS: Add maintainer for HiSilicon GPIO driver

Here add maintainer information for HiSilicon GPIO driver.

Signed-off-by: Luo Jiaxing <luojiaxing@huawei.com>
Link: https://lore.kernel.org/r/1607934255-52544-3-git-send-email-luojiaxing@huawei.com


[Dropped some dead code when applying]
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>