drm/mediatek: handle events when enabling/disabling crtc

drm/mediatek: handle events when enabling/disabling crtc

[ Upstream commit 411f5c1eacfebb1f6e40b653d29447cdfe7282aa ]

The driver currently handles vblank events only when updating planes on
an already enabled CRTC. The atomic update API however allows requesting
an event when enabling or disabling a CRTC. This currently leads to
event objects being leaked in the kernel and to events not being sent
out. Fix it.

Signed-off-by: Bibby Hsieh <bibby.hsieh@mediatek.com>
Signed-off-by: CK Hu <ck.hu@mediatek.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>