rcutorture: Add a stall_cpu_repeat module parameter

rcutorture: Add a stall_cpu_repeat module parameter

This commit adds an stall_cpu_repeat kernel, which is also the
rcutorture.stall_cpu_repeat boot parameter, to test repeated CPU stalls.
Note that only the first stall will pay attention to the stall_cpu_irqsoff
module parameter.  For the second and subsequent stalls, interrupts will
be enabled.  This is helpful when testing the interaction between RCU
CPU stall warnings and CSD-lock stall warnings.

Reported-by: Rik van Riel <riel@surriel.com>
Signed-off-by: "Paul E. McKenney" <paulmck@kernel.org>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>