rcutorture: Use "all" and "N" in "nohz_full" and "rcu_nocbs"

This commit uses the shiny new "all" and "N" cpumask options to decouple
the "nohz_full" and "rcu_nocbs" kernel boot parameters in the TREE04.boot
and TREE08.boot files from the CONFIG_NR_CPUS options in the TREE04 and
TREE08 files.
Reported-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

tools/testing/selftests/rcutorture/configs/rcu/TREE04.boot

-rcutree.rcu_fanout_leaf=4 nohz_full=1-7
+rcutree.rcu_fanout_leaf=4 nohz_full=1-N

tools/testing/selftests/rcutorture/configs/rcu/TREE08.boot

 rcupdate.rcu_self_test=1
 rcutree.rcu_fanout_exact=1
-rcu_nocbs=0-7
+rcu_nocbs=all