perf stat: Support JSON metrics in perf stat

Add generic support for standalone metrics specified in JSON files to
perf stat. A metric is a formula that uses multiple events to compute a
higher level result (e.g. IPC).

Previously metrics were always tied to an event and automatically
enabled with that event. But now change it that we can have standalone
metrics. They are in the same JSON data structure as events, but don't
have an event name.

We also allow to organize the metrics in metric groups, which allows a
short cut to select several related metrics at once.

Add a new -M / --metrics option to perf stat that adds the metrics or
metric groups specified.

Add the core code to manage and parse the metric groups. They are
collected from the JSON data structures into a separate rblist.  When
computing shadow values look for metrics in that list.  Then they are
computed using the existing saved values infrastructure in stat-shadow.c

The actual JSON metrics are in a separate pull request.

  % perf stat -M Summary --metric-only -a sleep 1

   Performance counter stats for 'system wide':

  Instructions   CLKS          CPU_Utilization  GFLOPs   SMT_2T_Utilization   Kernel_Utilization
  317614222.0    1392930775.0  0.0              0.0      0.2                  0.1

       1.001497549 seconds time elapsed

  % perf stat -M GFLOPs flops

   Performance counter stats for 'flops':

     3,999,541,471  fp_comp_ops_exe.sse_scalar_single #  1.2 GFLOPs   (66.65%)
                14  fp_comp_ops_exe.sse_scalar_double                 (66.65%)
                 0  fp_comp_ops_exe.sse_packed_double                 (66.67%)
                 0  fp_comp_ops_exe.sse_packed_single                 (66.70%)
                 0  simd_fp_256.packed_double                         (66.70%)
                 0  simd_fp_256.packed_single                         (66.67%)
                 0  duration_time

       3.238372845 seconds time elapsed

v2: Add missing header file
v3: Move find_map to pmu.c

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/20170831194036.30146-7-andi@firstfloor.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>