dt-bindings: mediatek: add mt7623 display-nodes

mt7623 uses mt2701/mt8173 for drm, but have own compatibles

Signed-off-by: Frank Wunderlich <frank-w@public-files.de>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>