perf list: Add metric groups to perf list

Add code to perf list to print metric groups, and metrics
that don't have an event name. The metricgroup code collects
the eventgroups and events into a rblist, and then prints
them according to the configured filters.

The metricgroups are printed by default, but can be
limited by perf list metric or perf list metricgroup

  % perf list metricgroup
  ..
  Metric Groups:

  DSB:
    DSB_Coverage
          [Fraction of Uops delivered by the DSB (aka Decoded Icache; or Uop Cache)]
  FLOPS:
    GFLOPs
          [Giga Floating Point Operations Per Second]
  Frontend:
    IFetch_Line_Utilization
          [Rough Estimation of fraction of fetched lines bytes that were likely consumed by program instructions]
  Frontend_Bandwidth:
    DSB_Coverage
          [Fraction of Uops delivered by the DSB (aka Decoded Icache; or Uop Cache)]
  Memory_BW:
    MLP
          [Memory-Level-Parallelism (average number of L1 miss demand load when there is at least 1 such miss)]

v2: Check return value of asprintf to fix warning on FC26
Fix key in lookup/addition for the groups list

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/20170831194036.30146-8-andi@firstfloor.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>