perf stat: Refactor aggregation code

Refactor aggregation code by introducing a single aggr_mode variable and an
enum for aggregation.

Also refactor cpumap code having to do with cpu to socket mappings. All in
preparation for extended modes, such as cpu -> core.

Also fix socket aggregation and ensure that sockets are printed in increasing
order.

Signed-off-by: Stephane Eranian <eranian@google.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung.kim@lge.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1360846649-6411-2-git-send-email-eranian@google.com


[ committer note: Fixup conflicts with a7e191c3 "--repeat forever" and
  acf28922 "Use perf_evlist__prepare/start_workload()" ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>