i386: Replace uint32_t* with FeatureWord on feature getter/setter

i386: Replace uint32_t* with FeatureWord on feature getter/setter

Instead of passing a pointer to the feature property getter and
setter functions, pass a FeatureWord enum so they can perform
other actions related to the feature flag.

This will be used to add a new "user_features" field to keep
track of features that were explicitly set by the user.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20170327144815.8043-2-ehabkost@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Tested-by: Jiri Denemark <jdenemar@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>