travis.yml: Update the list of s390x tests

With the new QEMU from Ubuntu Focal, we can now run more tests with TCG.

Message-Id: <20200924161612.144549-10-thuth@redhat.com>
Acked-by: Cornelia Huck <cohuck@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>