pinctrl: mediatek: Add pinctrl driver for mt8192

This commit includes pinctrl driver for mt8192.

Signed-off-by: Zhiyong Tao <zhiyong.tao@mediatek.com>
Acked-by: Sean Wang <sean.wang@kernel.org>
Link: https://lore.kernel.org/r/20200817001702.1646-4-zhiyong.tao@mediatek.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>