drm/mediatek: Move mtk_crtc_finish_page_flip() to ddp_cmdq_cb()

mtk_crtc_finish_page_flip() is used to notify userspace that a
page flip has been completed, allowing userspace to free the frame
buffer of the last frame and commit the next frame.

In MediaTek's hardware design for configuring display hardware by using
GCE, `DRM_EVENT_FLIP_COMPLETE` should be notified to userspace after
GCE has finished configuring all display hardware settings for each
atomic_commit().

Currently, mtk_crtc_finish_page_flip() cannot guarantee that GCE has
configured all the display hardware settings of the last frame.
Therefore, to increase the accuracy of the timing for notifying
`DRM_EVENT_FLIP_COMPLETE` to userspace, mtk_crtc_finish_page_flip()
should be moved to ddp_cmdq_cb().

Fixes: 7f82d9c4 ("drm/mediatek: Clear pending flag when cmdq packet is done")
Signed-off-by: Jason-JH.Lin <jason-jh.lin@mediatek.com>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20241211034716.29241-1-jason-jh.lin@mediatek.com/


Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>