pinctrl: add lock in mtk_rmw function.

pinctrl: add lock in mtk_rmw function.

When multiple threads operate on the same register resource
which include multiple pin, It will make the register resource
wrong to control. So we add lock to avoid the case.

Signed-off-by: Zhiyong Tao <zhiyong.tao@mediatek.com>
Link: https://lore.kernel.org/r/20210321033150.15380-2-zhiyong.tao@mediatek.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>