drm/dp-helper: Deprecate old i2c-over-dp_aux heleprs

Only gma500 is still using this, once that's converted we can kill all
this code. If that conversion doesn't happen soonish I think we should
just move this helper code into the gma500 driver itself to avoid
abuse from new drivers.

Cc: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Cc: Alan Cox <alan@linux.intel.com>
Cc: Thierry Reding <treding@nvidia.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_dp_helper.c

@@ -213,6 +213,10 @@ i2c_dp_aux_prepare_bus(struct i2c_adapter *adapter)
  *
  * RETURNS:
  * 0 on success, -ERRNO on failure.
+ *
+ * IMPORTANT:
+ * This interface is deprecated, please switch to the new dp aux helpers and
+ * drm_dp_aux_register_i2c_bus().
  */
 int
 i2c_dp_aux_add_bus(struct i2c_adapter *adapter)