define KVM_CAP_DEVICE_DEASSIGNMENT and KVM_DEASSIGN_PCI_DEVICE
for device deassignment.

the ioctl has been already implemented in the
commit: 0a920356Acked-by: NMark McLoughlin <markmc@redhat.com>
Signed-off-by: NWeidong Han <weidong.han@intel.com>
Signed-off-by: NAvi Kivity <avi@redhat.com>