media: dt-binding: mediatek: add bindings for MediaTek MDP3 components

This patch adds DT binding documents for Media Data Path 3 (MDP3)
a unit in multimedia system combined with several components and
used for scaling and color format convert.

Signed-off-by: Moudy Ho <moudy.ho@mediatek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>