drm/i915: Remove AUX CH sanitation

drm/i915: Remove AUX CH sanitation

Stop with the VBT AUX CH sanitation, and instead just check
that the appropriate AUX CH is still available when initializing
a DP/TC port.

The reason being that we want to start initializing ports in
VBT order to deal with VBTs that declare child devices with
seemingly conflicting ports. As the encoder initialization can
fail for other reasons (at least for eDP+AUX) we can't know
upfront which way the conflicts should be resolved.

Note that the old way of sanitizing gave priority to the last
port declared in the VBT, but now we sort of do the opposite by
favoring the first encoder to successfully initialize. The reason
for the old "last port wins" preference was eg. Asrock B250M-HDV
where port A (eDP) and port E (DP->VGA) have an AUX CH conflict
and we need to prefer port E. However with the new way port A (eDP)
will be probed first, but will fail to probe due to HPD and thus
port E will still win in the end.

v2: Pimp the commit message (Jani)

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230630155846.29931-5-ville.syrjala@linux.intel.com