drm/i915: Boost GPU frequency if we detect outstanding pageflips

If we hit a vblank and see that have a pageflip queue but not yet
processed, ensure that the GPU is running at maximum in order to clear
the backlog. Pageflips are only queued for the following vblank, if we
miss it, there will be a visible stutter. Boosting the GPU frequency
doesn't prevent us from missing the target vblank, but it should help
the subsequent frames hitting theirs.

v2: Reorder vblank vs flip-complete so that we only check for a missed
flip after processing the completion events, and avoid spurious boosts.

v3: Rename missed_vblank
v4: Rebase
v5: Cancel the outstanding work in runtime suspend
v6: Rebase
v7: Rebase required fixing

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Deepak S<deepak.s@linux.intel.com>
Reviewed-by: Deepak <S&lt;deepak.s@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>