arm64: dts: mt8173: Add display subsystem related nodes

This patch adds the device nodes for the DISP function blocks
comprising the display subsystem.

Signed-off-by: CK Hu <ck.hu@mediatek.com>
Signed-off-by: Cawa Cheng <cawa.cheng@mediatek.com>
Signed-off-by: Jie Qiu <jie.qiu@mediatek.com>
Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>