vfio/pci: Revert nvlink removal uAPI breakage

Revert the uAPI changes from the below commit with notice that these
regions and capabilities are no longer provided.

Fixes: b392a198 ("vfio/pci: remove vfio_pci_nvlink2")
Reported-by: Greg Kurz <groug@kaod.org>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Tested-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Message-Id: <162014341432.3807030.11054087109120670135.stgit@omen>