futex: run with more threads

The futex runs currently defaults to only the same number
of cpus the system has. Change this to iterate from 64 to 1024
threads. This produces longer runs and more relevant data
than using lower count of threads. Results are displayed grouped
by workload:
                                                             a                     b
Tput hash (private futex) (64 threads)     289606.00 (  0.00%)   288188.00 ( -0.49%)
Tput hash (private futex) (128 threads)    145565.00 (  0.00%)   146253.00 (  0.47%)
Tput hash (private futex) (256 threads)     73129.00 (  0.00%)    73057.00 ( -0.10%)
Tput hash (private futex) (512 threads)     36703.00 (  0.00%)    36546.00 ( -0.43%)
Tput hash (private futex) (1024 threads)    18237.00 (  0.00%)    18223.00 ( -0.08%)

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>