drm/dp_mst: Deprecate drm_dp_find_vcpi_slots()

Because we have drm_dp_atomic_find_vcpi_slots(), which actually takes
care to update the atomic state of the MST topology, prints valuable
debugging output, and actually takes references to the ports it's
checking! This explains some incorrect usage I've been seeing across the
tree...
Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20181023231251.16883-2-lyude@redhat.com

drivers/gpu/drm/drm_dp_mst_topology.c

@@ -2569,9 +2569,16 @@ struct edid *drm_dp_mst_get_edid(struct drm_connector *connector, struct drm_dp_
 EXPORT_SYMBOL(drm_dp_mst_get_edid);
 
 /**
- * drm_dp_find_vcpi_slots() - find slots for this PBN value
+ * drm_dp_find_vcpi_slots() - Find VCPI slots for this PBN value
  * @mgr: manager to use
  * @pbn: payload bandwidth to convert into slots.
+ *
+ * Calculate the number of VCPI slots that will be required for the given PBN
+ * value. This function is deprecated, and should not be used in atomic
+ * drivers.
+ *
+ * RETURNS:
+ * The total slots required for this port, or error.
  */
 int drm_dp_find_vcpi_slots(struct drm_dp_mst_topology_mgr *mgr,
 			   int pbn)