drm/i915: Perform primary enable/disable atomically with sprite updates

Move the primary plane enable/disable to occur atomically with the
sprite update that caused the primary plane visibility to change.

FBC and IPS enable/disable is left to happen well before or after
the primary plane change.

v2: Pass intel_crtc instead of drm_crtc (Daniel)

Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Sourab Gupta <sourabgupta@gmail.com>
Reviewed-by: Akash Goel <akash.goels@gmail.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>