drm/i915: Update atomic modeset state synchronously, v2.

drm/i915: Update atomic modeset state synchronously, v2.

All of this state should be updated as soon as possible. It shouldn't be
done later because then future updates may not depend on it.

Changes since v1:
- Move the modeset update to before drm_atomic_state_get. (Ville)

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1478609742-13603-10-git-send-email-maarten.lankhorst@linux.intel.com
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>