target-i386: Remove underscores from feat_names arrays

Instead of translating the feature name entries when adding
property names, store the actual property names in the feature
name array.

For reference, here is the full list of functions that use
FeatureWordInfo::feat_names:

* x86_cpu_get_migratable_flags(): not affected, as it just
  check for non-NULL values.
* report_unavailable_features(): informative only. It will
  start printing feature names with hyphens.
* x86_cpu_list(): informative only. It will start printing
  feature names with hyphens
* x86_cpu_register_feature_bit_props(): not affected, as it
  was already calling feat2prop(). Now we can remove the
  feat2prop() calls safely.

So, the only user-visible effect of this patch are the new names
being used in help and error messages for users.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
