perf list: Support matching by topic

Add support in perf list topic to only show events belonging to a
specific vendor events topic. For example the following works now:

  % perf list frontend
  List of pre-defined events (to be used in -e):

    stalled-cycles-frontend OR idle-cycles-frontend    [Hardware event]

    stalled-cycles-frontend OR cpu/stalled-cycles-frontend/ [Kernel PMU event]

  frontend:
    dsb2mite_switches.count
         [Decode Stream Buffer (DSB)-to-MITE switches]
    dsb2mite_switches.penalty_cycles
         [Decode Stream Buffer (DSB)-to-MITE switch true penalty cycles]
    dsb_fill.exceed_dsb_lines
         [Cycles when Decode Stream Buffer (DSB) fill encounter more than 3 Decode Stream Buffer (DSB)
          lines]
    icache.hit
         [Number of Instruction Cache, Streaming Buffer and Victim Cache Reads. both cacheable and
          noncacheable, including UC fetches]
  ...

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/1476902724-9586-2-git-send-email-andi@firstfloor.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>