dt-bindings: pinctrl: add binding for MT7988 SoC

This adds bindings for MT7988 pinctrl driver.

Signed-off-by: Frank Wunderlich <[email protected]>
Reviewed-by: AngeloGioacchino Del Regno <[email protected]>
Reviewed-by: Rob Herring (Arm) <[email protected]>
Link: https://lore.kernel.org/[email protected]
Signed-off-by: Linus Walleij <[email protected]>

Author: frank-w