Some more perf tuning.
Some more perf tuning.

* In case of huge number of small workgroups, scale up
  the amount of work we fetch in get_wg_index_range()
  linearly to CU number, this helps avoiding lock
  contention in get_wg_index_range() with manycore CPUs.

Oblomov/pocl,Oblomov/pocl,pocl/pocl,franz/pocl,pocl/pocl,pocl/pocl,pocl/pocl,rjodin/pocl,franz/pocl,franz/pocl,Oblomov/pocl,rjodin/pocl,rjodin/pocl,franz/pocl,Oblomov/pocl,pocl/pocl,Oblomov/pocl,franz/pocl,rjodin/pocl