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/kernel/irq.c

@@ -60,6 +60,7 @@ static const struct irq_class intrclass_names[] = {
 	[IOINT_CSC]  = {.name = "CSC", .desc = "[I/O] CHSC Subchannel"},
 	[IOINT_PCI]  = {.name = "PCI", .desc = "[I/O] PCI Interrupt" },
 	[IOINT_MSI] =  {.name = "MSI", .desc = "[I/O] MSI Interrupt" },
+	[IOINT_VIR]  = {.name = "VIR", .desc = "[I/O] Virtual I/O Devices"},
 	[NMI_NMI]    = {.name = "NMI", .desc = "[NMI] Machine Check"},
 };