tools/power turbostat: Increase the limit for fd opened

When running turbostat, a system with 512 cpus reaches the limit for
maximum number of file descriptors that can be opened. To solve this
problem, the limit is raised to 2^15, which is a large enough number.

Below data is collected from AMD server systems while running turbostat:

|-----------+-------------------------------|
| # of cpus | # of opened fds for turbostat |
|-----------+-------------------------------|
| 128       | 260                           |
|-----------+-------------------------------|
| 192       | 388                           |
|-----------+-------------------------------|
| 512       | 1028                          |
|-----------+-------------------------------|

So, the new max limit would be sufficient up to 2^14 cpus (but this
also depends on how many counters are enabled).

Reviewed-by: Doug Smythies <dsmythies@telus.net>
Tested-by: Doug Smythies <dsmythies@telus.net>
Signed-off-by: Wyes Karny <wyes.karny@amd.com>
Signed-off-by: Len Brown <len.brown@intel.com>