tools/memory-model/README: Update klitmus7 compat table

EXPORT_SYMBOL of do_exec() was removed in v5.17.  Unfortunately,
kernel modules from klitmus7 7.56 have do_exec() at the end of
each kthread.

herdtools7 7.56.1 has addressed the issue.

Update the compatibility table accordingly.

Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Cc: Luc Maranget <luc.maranget@inria.fr>
Cc: Jade Alglave <j.alglave@ucl.ac.uk>
Cc: stable@vger.kernel.org # v5.17+
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>