qemu: remove panic dev models s390 and pseries when migrating
    
    The panic devices with models s390 and pseries are autogenerated.
    For backwards compatibility reasons the devices are to be removed
    when migrating.
    
    Signed-off-by: Boris Fiuczynski <fiuczy@linux.vnet.ibm.com>
    Signed-off-by: Ján Tomko <jtomko@redhat.com>