drm/i915: Rename hw state checker to hw state verifier.

drm/i915: Rename hw state checker to hw state verifier.

Check functions are used by atomic to see if the new state will
be allowed. There's also a hw state checker which checks afterwards
that the committed state is correct. Rename it to hw state verifier
to reduce some confusion.

Suggested-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/56FB8785.8020506@linux.intel.com
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>