qemu: introduce vfio-ccw capability

qemu: introduce vfio-ccw capability

Let us introduce the capability vfio-ccw for supporting the basic
channel I/O passthrough, which have been introduced in QEMU 2.10. The
current focus is to support dasd-eckd (cu_type/dev_type = 0x3990/0x3390)
as the target device.

Let us also introduce the capability QEMU_CAPS_CCW_CSSID_UNRESTRICTED
for virtual-css-bridge. This capability is based on the
cssid-unrestricted property which exists if QEMU no longer enforces
cssid restrictions based on ccw device types.

Vfio-ccw capability is dependent on the hidden virtual-css-bridge, so
that we are able to probe for the cssid-unrestriced property to make
sure the devices are visible to non-mcss-e enabled guests.

Signed-off-by: Shalini Chellathurai Saroja <shalini@linux.vnet.ibm.com>
Reviewed-by: Bjoern Walk <bwalk@linux.ibm.com>
Reviewed-by: Boris Fiuczynski <fiuczy@linux.ibm.com>
Reviewed-by: John Ferlan <jferlan@redhat.com>