Added to 'query-command-line-options' in qemu commit 5559716c98
("util/qemu-config: Add loadparm to qemu machine_opts") released in
qemu-v2.10.0 but makes sense for s390 only. Treat it the same as the
keywrap capabilities in previous commit.
Signed-off-by: Peter Krempa <pkrempa@redhat.com> Reviewed-by: Ján Tomko <jtomko@redhat.com>