drm: encapsulate crtc->set_config calls

With refcounting we need to adjust framebuffer refcounts at each
callsite - much easier to do if they all call the same little helper
function.

Reviewed-by: Rob Clark <rob@ti.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index 00d78b5..665289a6 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -985,6 +985,7 @@
 			    void *data, struct drm_file *file_priv);
 extern int drm_mode_getconnector(struct drm_device *dev,
 			      void *data, struct drm_file *file_priv);
+extern int drm_mode_set_config_internal(struct drm_mode_set *set);
 extern int drm_mode_setcrtc(struct drm_device *dev,
 			    void *data, struct drm_file *file_priv);
 extern int drm_mode_getplane(struct drm_device *dev,