Normally SE Linux doesn't need any special mount option. user_xattr is for applications that want to create xattrs named "user.something" and doesn't apply to "security.selinux".
Unless QEMU does something different in this regard then you should not need this.
Of course xattrs are usually a good thing and I can't think of any harm in having them enabled. But I am not aware of it being required for SE Linux.