perf stat: Support metrics in --per-core/socket mode

perf stat: Support metrics in --per-core/socket mode

Enable metrics printing in --per-core / --per-socket mode. We need to
save the shadow metrics in a unique place. Always use the first CPU in
the aggregation. Then use the same CPU to retrieve the shadow value
later.

Example output:

  % perf stat --per-core -a ./BC1s

   Performance counter stats for 'system wide':

  S0-C0 2   2966.020381 task-clock (msec) #   2.004 CPUs utilized  (100.00%)
  S0-C0 2            49 context-switches  #   0.017 K/sec          (100.00%)
  S0-C0 2             4 cpu-migrations    #   0.001 K/sec          (100.00%)
  S0-C0 2           467 page-faults       #   0.157 K/sec
  S0-C0 2 4,599,061,773 cycles            #   1.551 GHz            (100.00%)
  S0-C0 2 9,755,886,883 instructions      #   2.12  insn per cycle (100.00%)
  S0-C0 2 1,906,272,125 branches          # 642.704 M/sec          (100.00%)
  S0-C0 2    81,180,867 branch-misses     #   4.26% of all branches
  S0-C1 2   2965.995373 task-clock (msec) #   2.003 CPUs utilized  (100.00%)
  S0-C1 2            62 context-switches  #   0.021 K/sec          (100.00%)
  S0-C1 2             8 cpu-migrations    #   0.003 K/sec          (100.00%)
  S0-C1 2           281 page-faults       #   0.095 K/sec
  S0-C1 2     6,347,290 cycles            #   0.002 GHz            (100.00%)
  S0-C1 2     4,654,156 instructions      #   0.73  insn per cycle (100.00%)
  S0-C1 2       947,121 branches          #   0.319 M/sec          (100.00%)
  S0-C1 2        37,322 branch-misses     #   3.94% of all branches

         1.480409747 seconds time elapsed

v2: Rebase to older patches
v3: Document shadow cpus. Fix aggr_get_id argument. Fix -A shadows (Jiri)

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/1456785386-19481-4-git-send-email-andi@firstfloor.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>