[S390] qdio: fix check for running under z/VM

The check whether qdio runs under z/VM was incorrect since SIGA-Sync is not
set if the device runs with QIOASSIST. Use MACHINE_IS_VM instead to prevent
polling under z/VM.

Merge qdio_inbound_q_done and tiqdio_is_inbound_q_done.

Signed-off-by: Jan Glauber <jang@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>