drm/i915/chv: Add DPFLIPSTAT register bits for Cherryview

CHV has pipe C and PSR which cause changes to DPFLIPSTAT.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Rafael Barbalho <rafael.barbalho@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>