QEMU on S390 (since v2.11) can support virtio input ccw devices.
So build the qemu command line for ccw devices.

Also add test cases for virtio-{keyboard, mouse, tablet}-ccw.
Signed-off-by: NFarhan Ali <alifm@linux.vnet.ibm.com>
Signed-off-by: NBoris Fiuczynski <fiuczy@linux.vnet.ibm.com>