dt-bindings: pinctrl: mt8195: add pinctrl file and binding document

1. This patch adds pinctrl file for mt8195.
2. This patch adds mt8195 compatible node in binding document.

Signed-off-by: Zhiyong Tao <zhiyong.tao@mediatek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210413055702.27535-2-zhiyong.tao@mediatek.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>