drm/i915: Fix platform default aux ch for skl

SKL/derivatives have DDI E but no AUX E, so we need to pick
another aux ch as the platform default. DDI E is more or less
the other half of DDI A, so we pick AUX A.

In all other cases we should have a corresponding aux ch for
each DDI.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230216231312.32664-3-ville.syrjala@linux.intel.com


Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>