drm/i915/bios: limit default outputs by platform on missing VBT

Pre-DDI and non-CHV aren't using the information created here anyway, so
don't bother setting the defaults for them. This should be a
non-functional change, but is separated here to catch any regressions in
a single commit.

Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/41526a4eee5fb0de8d7f1ffe4c09965b63ccbaa8.1615998927.git.jani.nikula@intel.com