arm64: dts: mediatek: mt8173-elm: Move display to ps8640 auxiliary bus

Move the display to an aux-bus subnode of the PS8640 eDP bridge.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20230111140724.294533-1-angelogioacchino.delregno@collabora.com


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