This sync API will be used by the CPU hotplug code to wait for the CPU to
completely get removed before flagging the failure to the device_add
command.

Sync version of this call is needed to correctly recover from CPU
realization failures when ->plug() handler fails.
Signed-off-by: NBharata B Rao <bharata@linux.vnet.ibm.com>
Reviewed-by: NDavid Gibson <david@gibson.dropbear.id.au>
Acked-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NDavid Gibson <david@gibson.dropbear.id.au>