target-i386: Loop-based feature word filtering in TCG mode

Instead of manually filtering each feature word, add a tcg_features
field to FeatureWordInfo, and use that field to filter all feature words
in TCG mode.

Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>
