rcutorture: Abstract torture_param()

Create a torture_param() macro and apply it to rcutorture in order to
save a few lines of code.  This same macro may be applied to other
torture frameworks.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --cc include/linux/torture.h
Simple merge

diff --cc kernel/rcu/rcutorture.c
Simple merge