arm64: dts: mediatek: mt8186: Add ADSP mailbox nodes

Add ADSP mailbox node for MT8186 SoC.

Signed-off-by: Allen-KH Cheng <allen-kh.cheng@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20230118091829.755-5-allen-kh.cheng@mediatek.com


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