hazptrtorture: Add irq_release to release hazptr from irq

This commit adds the irq_release module parameter, which specifies how
often hazard pointers will be released from an smp_call_function_single()
handler.  For example, a value of 10 would result in one of of ten
hazard-pointer acquisitions taking place in a handler, and probably also
death by excessive numbers of handlers.  A value of zero disables, and
a value of -1 makes the frequency decrease as a function of the number
of CPUs.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>