drm/i915: Only call commit_planes when there are things to commit.

The atomic helpers set planes_changed on a crtc_state if there is
any plane_state bound to that crtc. If there's none and there is
no pipe update required the crtc has nothing to update, so vblank
evasion can be skipped.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -13153,7 +13153,8 @@ static int intel_atomic_commit(struct drm_device *dev,
 		if (!modeset)
 			intel_pre_plane_update(intel_crtc);
 
-		if (crtc->state->active)
+		if (crtc->state->active &&
+		    (crtc->state->planes_changed || update_pipe))
 			drm_atomic_helper_commit_planes_on_crtc(crtc_state);
 
 		if (put_domains)