vfio/ccw: Use vfio_[attach/detach]_device

vfio/ccw: Use vfio_[attach/detach]_device

Let the vfio-ccw device use vfio_attach_device() and
vfio_detach_device(), hence hiding the details of the used
IOMMU backend.

Note that the migration reduces the following trace
"vfio: subchannel %s has already been attached" (featuring
cssid.ssid.devid) into "device is already attached"

Also now all the devices have been migrated to use the new
vfio_attach_device/vfio_detach_device API, let's turn the
legacy functions into static functions, local to container.c.

Signed-off-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Yi Liu <yi.l.liu@intel.com>
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>