The kvmvapic device is only usable when created by
apic_common_realize(), not using -device. Remove the
user_creatable flag from the device class.

Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Marcel Apfelbaum <marcel@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Acked-by: Marcel Apfelbaum <marcel@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20170503203604.31462-10-ehabkost@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>