KVM: s390: Add a channel I/O based virtio transport driver.

Add a driver for kvm guests that matches virtual ccw devices provided
by the host as virtio bridge devices.

These virtio-ccw devices use a special set of channel commands in order
to perform virtio functions.

Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>
Reviewed-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

arch/s390/include/asm/irq.h

@@ -35,6 +35,7 @@ enum interruption_class {
 	IOINT_CSC,
 	IOINT_PCI,
 	IOINT_MSI,
+	IOINT_VIR,
 	NMI_NMI,
 	NR_IRQS,
 };