[PATCH] drm/vc4: Make pageflip completion handling more robust.

Mario Kleiner writes: > Protect both the setup of the pageflip event and the > latching of the new requested displaylist head pointer > by the event lock, so we can't get into a situation > where vc4_atomic_flush latches the new display list via > HVS_WRITE, then immediately gets preempted before

[PATCH] drm/vc4: Make pageflip completion handling more robust.

Protect both the setup of the pageflip event and the latching of the new requested displaylist head pointer by the event lock, so we can't get into a situation where vc4_atomic_flush latches the new display list via HVS_WRITE, then immediately gets preempted before queueing the pageflip event, then