Now that helpers are available in xen_backend, use them throughout all
Xen PV backends.
Signed-off-by: NPaul Durrant <paul.durrant@citrix.com>
Acked-by: NAnthony Perard <anthony.perard@citrix.com>
Signed-off-by: NStefano Stabellini <sstabellini@kernel.org>