soc / drm: mediatek: Move DDP component defines into mtk-mmsys.h

MMSYS is the driver which controls the routing of these DDP components,
so the definition of the mtk_ddp_comp_id enum should be placed in mtk-mmsys.h

Signed-off-by: Yongqiang Niu <yongqiang.niu@mediatek.com>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Reviewed-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>
Link: https://lore.kernel.org/r/20201006193320.405529-2-enric.balletbo@collabora.com


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