pinctrl: mediatek: update pinmux definitions for mt6779

Add devicetree bindings for Mediatek mt6779 SoC Pin Controller.

Signed-off-by: Mars Cheng <mars.cheng@mediatek.com>
Signed-off-by: Andy Teng <andy.teng@mediatek.com>
Signed-off-by: Hanks Chen <hanks.chen@mediatek.com>
Acked-by: Sean Wang <sean.wang@kernel.org>
Link: https://lore.kernel.org/r/1595503197-15246-2-git-send-email-hanks.chen@mediatek.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>