drm/i915: Move to atomic plane helpers (v9)

Switch plane handling to use the atomic plane helpers.  This means that
rather than provide our own implementations of .update_plane() and
.disable_plane(), we expose the lower-level check/prepare/commit/cleanup
entrypoints and let the DRM core implement update/disable for us using
those entrypoints.

The other main change that falls out of this patch is that our
drm_plane's will now always have a valid plane->state that contains the
relevant plane state (initial state is allocated at plane creation).
The base drm_plane_state pointed to holds the requested source/dest
coordinates, and the subclassed intel_plane_state holds the adjusted
values that our driver actually uses.

v2:
 - Renamed file from intel_atomic.c to intel_atomic_plane.c (Daniel)
 - Fix a copy/paste comment mistake (Bob)

v3:
 - Use prepare/cleanup functions that we've already factored out
 - Use newly refactored pre_commit/commit/post_commit to avoid sleeping
   during vblank evasion

v4:
 - Rebase to latest di-nightly requires adding an 'old_state' parameter
   to atomic_update;

v5:
 - Must have botched a rebase somewhere and lost some work.  Restore
   state 'dirty' flag to let begin/end code know which planes to
   run the pre_commit/post_commit hooks for.  This would have actually
   shown up as broken in the next commit rather than this one.

v6:
 - Squash kerneldoc patch into this one.
 - Previous patches have now already taken care of most of the
   infrastructure that used to be in this patch.  All we're adding here
   now is some thin wrappers.

v7:
 - Check return of intel_plane_duplicate_state() for allocation
   failures.

v8:
 - Drop unused drm_plane_state -> intel_plane_state cast.  (Ander)
 - Squash in actual transition to plane helpers.  Significant
   refactoring earlier in the patchset has made the combined
   prep+transition much easier to swallow than it was in earlier
   iterations. (Ander)

v9:
 - s/track_fbs/disabled_planes/ in the atomic crtc flags.  The only fb's
   we need to update frontbuffer tracking for are those on a plane about
   to be disabled (since the atomic helpers never call prepare_fb() when
   disabling a plane), so the new name more accurately describes what
   we're actually tracking.

Testcase: igt/kms_plane
Testcase: igt/kms_universal_plane
Testcase: igt/kms_cursor_crc
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>