drm/nouveau: Use drm_fb_helper_output_poll_changed()

This driver can use drm_fb_helper_output_poll_changed() instead of
its own nouveau_fbcon_output_poll_changed().

Cc: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20171205182504.41923-8-noralf@tronnes.org

drivers/gpu/drm/nouveau/nouveau_fbcon.c

@@ -413,14 +413,6 @@ out:
 	return ret;
 }
 
-void
-nouveau_fbcon_output_poll_changed(struct drm_device *dev)
-{
-	struct nouveau_drm *drm = nouveau_drm(dev);
-	if (drm->fbcon)
-		drm_fb_helper_hotplug_event(&drm->fbcon->helper);
-}
-
 static int
 nouveau_fbcon_destroy(struct drm_device *dev, struct nouveau_fbdev *fbcon)
 {