Include CONFIG_DEVICES so that populate_vfio_info is instantiated for
CONFIG_VFIO.  Without it, the 'info migrate' command never returns
info about vfio.

Fixes: 43bd0bf3 ("migration: Move populate_vfio_info() into a separate file")
Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>