i386/cpu: Don't add unavailable_features to env->user_features

i386/cpu: Don't add unavailable_features to env->user_features

Features unavailable due to absent of their dependent features should
not be added to env->user_features. env->user_features only contains the
feature explicity specified with -feature/+feature by user.

Fixes: 99e24dbdaa68 ("target/i386: introduce generic feature dependency mechanism")
Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Message-Id: <20200713174436.41070-3-xiaoyao.li@intel.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>