drm/i915: Refactor work that can sleep out of commit (v7)

Once we integrate our work into the atomic pipeline, plane commit
operations will need to happen with interrupts disabled, due to vblank
evasion.  Our commit functions today include sleepable work, so those
operations need to be split out and run either before or after the
atomic register programming.

The solution here calculates which of those operations will need to be
performed during the 'check' phase and sets flags in an intel_crtc
sub-struct.  New intel_begin_crtc_commit() and
intel_finish_crtc_commit() functions are added before and after the
actual register programming; these will eventually be called from the
atomic plane helper's .atomic_begin() and .atomic_end() entrypoints.

v2: Fix broken sprite code split

v3: Make the pre/post commit work crtc-based to match how we eventually
    want this to be called from the atomic plane helpers.

v4: Some platforms that haven't had their watermark code reworked were
    waiting for vblank, then calling update_sprite_watermarks in their
    platform-specific disable code.  These also need to be flagged out
    of the critical section.

v5: Sprite plane test for primary show/hide should just set the flag to
    wait for pending flips, not actually perform the wait.  (Ander)

v6:
 - Rebase onto latest di-nightly; picks up an important runtime PM fix.
 - Handle 'wait_for_flips' flag in intel_begin_crtc_commit(). (Ander)
 - Use wait_for_flips flag for primary plane update rather than
   performing the wait in the check routine.
 - Added kerneldoc to pre_disable/post_enable functions that are no
   longer static.  (Ander)
 - Replace assert_pipe_enabled() in intel_disable_primary_hw_plane()
   with an intel_crtc->active test; it turns out assert_pipe_enabled()
   grabs some mutexes and can sleep, which we can't do with interrupts
   disabled.

v7:
 - Check for fb != NULL when deciding whether the sprite plane hides the
   primary plane during a sprite update.  (PRTS)

Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Ander Conselvan de Oliveira <conselvan2@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>