drm/i915: Don't use struct intel_set_config *_changed flags

Use the similar fields in crtc_state instead, so that this code can be
moved to our future implementation of atomic_check().

Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>