drm/i915: Revert async unpin and nonblocking atomic commit

This reverts the following patches:

d55dbd06 drm/i915: Allow nonblocking update of pageflips.
15c86bdb drm/i915: Check for unpin correctness.
95c2ccdc Reapply "drm/i915: Avoid stalling on pending flips for legacy cursor updates"
a6747b73 drm/i915: Make unpin async.
03f476e1 drm/i915: Prepare connectors for nonblocking checks.
2099deff drm/i915: Pass atomic states to fbc update functions.
ee7171af drm/i915: Remove reset_counter from intel_crtc.
2ee004f7 drm/i915: Remove queue_flip pointer.
b8d2afae drm/i915: Remove use_mmio_flip kernel parameter.
8dd634d9 drm/i915: Remove cs based page flip support.
143f73b3 drm/i915: Rework intel_crtc_page_flip to be almost atomic, v3.
84fc494b drm/i915: Add the exclusive fence to plane_state.
6885843a drm/i915: Convert flip_work to a list.
aa420ddd drm/i915: Allow mmio updates on all platforms, v2.
afee4d87 Revert "drm/i915: Avoid stalling on pending flips for legacy cursor updates"

"drm/i915: Allow nonblocking update of pageflips" should have been
split up, misses a proper commit message and seems to cause issues in
the legacy page_flip path as demonstrated by kms_flip.

"drm/i915: Make unpin async" doesn't handle the unthrottled cursor
updates correctly, leading to an apparent pin count leak. This is
caught by the WARN_ON in i915_gem_object_do_pin which screams if we
have more than DRM_I915_GEM_OBJECT_MAX_PIN_COUNT pins.

Unfortuantely we can't just revert these two because this patch series
came with a built-in bisect breakage in the form of temporarily
removing the unthrottled cursor update hack for legacy cursor ioctl.
Therefore there's no other option than to revert the entire pile :(

There's one tiny conflict in intel_drv.h due to other patches, nothing
serious.

Normally I'd wait a bit longer with doing a maintainer revert, but
since the minimal set of patches we need to revert (due to the bisect
breakage) is so big, time is running out fast. And very soon
(especially after a few attempts at fixing issues) it'll be really
hard to revert things cleanly.

Lessons learned:
- Not a good idea to rush the review (done by someone fairly new to
  the area) and not make sure domain experts had a chance to read it.

- Patches should be properly split up. I only looked at the two
  patches that should be reverted in detail, but both look like the
  mix up different things in one patch.

- Patches really should have proper commit messages. Especially when
  doing more than one thing, and especially when touching critical and
  tricky core code.

- Building a patch series and r-b stamping it when it has a built-in
  bisect breakage is not a good idea.

- I also think we need to stop building up technical debt by
  postponing atomic igt testcases even longer. I think it's clear that
  there's enough corner cases in this beast that we really need to
  have the testcases _before_ the next step lands.

(cherry picked from commit 5a21b665
from drm-intel-next-queeud)

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Patrik Jakobsson <patrik.jakobsson@linux.intel.com>
Cc: John Harrison <John.C.Harrison@Intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Acked-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Acked-by: Dave Airlie <airlied@redhat.com>
Acked-by: Jani Nikula <jani.nikula@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>