arm64: dts: mediatek: Add MT6893 pinmux macro header file

Add the required macros for the pinmux nodes of the MT6893
Dimensity 1200 SoC.

Link: https://lore.kernel.org/r/20250410144044.476060-4-angelogioacchino.delregno@collabora.com


Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>