arm64: dts: mediatek: add pinctrl support for mt7986b

Add mt7986b pinctrl node

Signed-off-by: Sam Shih <sam.shih@mediatek.com>
Link: https://lore.kernel.org/r/20211122123552.8218-3-sam.shih@mediatek.com


Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>