perf bench: Fix futex bench to correct usage of affinity for machines with #CPUs > 1K

The 'perf bench futex' testcase fails on systems with more than 1K CPUs.

Testcase: perf bench futex all

Failure snippet:
<<>>Running futex/hash benchmark...

perf: pthread_create: No such file or directory
<<>>

All the futex benchmarks (ie hash, lock-api, requeue, wake,
wake-parallel), pthread_create is invoked in respective bench_futex_*
function. Though the logs shows direct failure from pthread_create,
strace logs showed that actual failure is from  "sched_setaffinity"
returning EINVAL (invalid argument).

This happens because the default mask size in glibc is 1024. To overcome
this 1024 CPUs mask size limitation of cpu_set_t, change the mask size
using the CPU_*_S macros.

Patch addresses this by fixing all the futex benchmarks to use CPU_ALLOC
to allocate cpumask, CPU_ALLOC_SIZE for size, and CPU_SET_S to set the
mask.

Reported-by: Disha Goel <disgoel@linux.vnet.ibm.com>
Reviewed-by: Srikar Dronamraju <srikar@li...>