Matt Roper authored Mar 04, 2015 and Daniel Vetter committed Mar 06, 2015

i915 was using the main atomic 'disable plane' to turn off sprite planes
during a CRTC disable.  This was problematic because it modified the
plane state, preventing us from recovering the original state later.
One such case was that during a DPMS OFF followed by a DPMS ON, any
sprite planes would not be restored properly.

Let's add a test that toggles DPMS off and on and ensures that the CRC
remains the same (i.e., planes are successfully restored unchanged).

Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>