Comment 2 for bug 1812360

Found it - this is the template they render into for x86 (working)
...
        <controller type='virtio-serial' index='0'>
          <address type='pci' domain='0x0000'
            bus='0x00' slot='0x05' function='0x0'/>
        </controller>
        <serial type='pty'>
          <log file="/var/log/libvirt/qemu/{name}-serial0.log" append="off" />
          <target port='0'/>
        </serial>
        <console type='pty'>
          <target type='serial' port='0'/>
        </console>
...

And this is the failing one for s390x:
...
      <devices>
        <serial type='pty'>
          <log file="/var/log/libvirt/qemu/{name}-serial0.log" append="off" />
          <target port='0'/>
        </serial>
        <console type='pty'>
          <target type='sclp' port='0'/>
          <alias name='console0'/>
        </console>
      </devices>
...

I guess they'd appreciate a suggested to work libvirt XML over a better qemu commandline