vmbus: Don't make QOM property registration conditional

vmbus: Don't make QOM property registration conditional

Having properties registered conditionally makes QOM type
introspection difficult.  Instead of skipping registration of the
"instanceid" property, always register the property but validate
its value against the instance id required by the class.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Acked-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Message-Id: <20201009200701.1830060-1-ehabkost@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>