perf tools: Use cpu/possible instead of cpu/kernel_max

The system's max configuration is represented by cpu/possible and
cpu/kernel_max can be huge (4096 vs. 128), so save space by keeping
smaller structures.

Signed-off-by: Don Zickus <dzickus@redhat.com>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/1396896924-129847-3-git-send-email-dzickus@redhat.com
Signed-off-by: Jiri Olsa <jolsa@redhat.com>