First step in removing dpms and validating atomic state.

There can still be a mismatch in the connector state because the dpms
callbacks are still used, but this can not happen immediately after a modeset.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Ander Conselvan de Oliveira <conselvan2@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>