xen: sync xs_wire.h header with upstream xen

Sync the xs_wire.h header file in Linux with the one in Xen.

Signed-off-by: Stefano Stabellini <stefano.stabellini@xilinx.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Link: https://lore.kernel.org/r/20220513211938.719341-1-sstabellini@kernel.org
Signed-off-by: Juergen Gross <jgross@suse.com>