drm/msm/dpu: fix "frame done" timeouts

Previously, dpu_crtc_frame_event_work() would try to aquire all the
modeset locks in order to check whether it can release bandwidth.  (If
we only have cmd-mode display, bandwidth can be released at frame-done
time.)

The problem with this is that it is also responsible for signalling
frame_done_comp, which dpu_crtc_commit_kickoff() waits on if there is
already a frame pending.  This is called in the msm_atomic_commit_tail()
path.. which means that for non-nonblock commits, at least some of the
modeset locks are already held.

Re-work this scheme to use a reference count to track our need to have
clocks enabled.  It is incremented for each atomic commit, and
decremented in the corresponding frame-done.  Additionally, any crtc
used in video mode hold an extra reference while they are enabled.  The
net effect is that we can determine in frame-done whether it is safe to
drop bandwidth without needing to aquire any modeset locks.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Sean Paul <sean@chromium.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>