arm64: dts: mediatek: mt6795: Add support for the CMDQ/GCE mailbox

In preparation for adding multimedia blocks, add the CMDQ/GCE mailbox.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20230412112739.160376-17-angelogioacchino.delregno@collabora.com


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