drm/vmwgfx: Properly flush cursor updates and page-flips

With the introduction of the new command buffer mechanism,
proper care wasn't taken to flush cursor image updates and
event-less screen-target page-flips.

Fix this by introducing explicit flush points.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>

drivers/gpu/drm/vmwgfx/vmwgfx_stdu.c

@@ -717,6 +717,8 @@ static int vmw_stdu_crtc_page_flip(struct drm_crtc *crtc,
 						   &event->event.tv_usec,
 						   true);
 		vmw_fence_obj_unreference(&fence);
+	} else {
+		vmw_fifo_flush(dev_priv, false);
 	}
 
 	return ret;