disp: msm: sde: flush all event thread work during CRTC disable

The API to flush the event thread is only flushing the
frame_event work queued on that thread but during disable
the vblank work must also be flushed. Instead of flushing
only frame_events work, flush all work queued on the event
thread worker. Also rename the API to more accurately describe
what it's doing.

Change-Id: Iaf248a2b1bafc9b9a15ae9447b72cdff07509a91
Signed-off-by: Steve Cohen <cohens@codeaurora.org>