Blacklist symbols in Xen probe-prohibited areas, so that user can see
these prohibited symbols in debugfs.

See also: a50480cb.
Signed-off-by: Andrea Righi <righi.andrea@gmail.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>