arm: dts: mt7623: add display subsystem related device nodes

Add display subsystem related device nodes for MT7623.

Signed-off-by: chunhui dai <chunhui.dai@mediatek.com>
Signed-off-by: Bibby Hsieh <bibby.hsieh@mediatek.com>
Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: Frank Wunderlich <frank-w@public-files.de>
Tested-by: Frank Wunderlich <frank-w@public-files.de>
Cc: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Link: https://lore.kernel.org/r/20200904110002.88966-4-linux@fw-web.de
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>