tools/power turbostat: fix bugs in --add option

When --add was used more than once, overflowed buffers
caused some counters to be stored on top of others,
corrupting the results.  Simplify the code by simply
reserving space for up to 16 added counters per each
cpu, core, package.

Per-cpu added counters were being printed only per-core.

Signed-off-by: Len Brown <len.brown@intel.com>