drm/i915: Get rid of dpms handling.

This is now done completely atomically.
Keep connectors_active for now, but make it mirror crtc_state->active.

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>