drm/atomic: Fix bookkeeping with TEST_ONLY, v3.

Commit ec9f932e
"drm/atomic: Cleanup on error properly in the atomic ioctl."
cleaned up some error paths, but didn't fix the TEST_ONLY path.
In the check only case plane->fb shouldn't be updated, and
the vblank events should be cleared as on failure.

Changes since v1:
- Fix -EDEADLK handling of vblank events too.
- Free state last with CHECK_ONLY.
Changes since v2:
- Add comment about freeing crtc_state->event with TEST_ONLY.
  (Daniel Stone)

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>