drm/i915: Give aux channels a better name

The aux ch is used for more than DDC, so let's give it a better
name. For maximum ease let's include both the AUX ch identifier
and the port identifier (for cases where the VBT has redefined
the relationship of the two).

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200123154542.12271-3-ville.syrjala@linux.intel.com


Reviewed-by: Matt Roper <matthew.d.roper@intel.com>