perf report: Add callchain value option

Now -g/--call-graph option supports how to display callchain values.
Possible values are 'percent', 'period' and 'count'.  The percent is
same as before and it's the default behavior.  The period displays the
raw period value rather than the percentage.  The count displays the
number of occurrences.

  $ perf report --no-children --stdio -g percent
  ...
    39.93%  swapper  [kernel.vmlinux]  [k] intel_idel
            |
            ---intel_idle
               cpuidle_enter_state
               cpuidle_enter
               call_cpuidle
               cpu_startup_entry
               |
               |--28.63%-- start_secondary
               |
                --11.30%-- rest_init

  $ perf report --no-children --show-total-period --stdio -g period
  ...
    39.93%   13018705  swapper  [kernel.vmlinux]  [k] intel_idel
            |
            ---intel_idle
               cpuidle_enter_state
               cpuidle_enter
               call_cpuidle
               cpu_startup_entry
               |
               |--9334403-- start_secondary
               |
                --3684302-- rest_init

  $ perf report --no-children --show-nr-samples --stdio -g count
  ...
    39.93%     80  swapper  [kernel.vmlinux]  [k] intel_idel
            |
            ---intel_idle
               cpuidle_enter_state
               cpuidle_enter
               call_cpuidle
               cpu_startup_entry
               |
               |--57-- start_secondary
               |
                --23-- rest_init

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1447047946-1691-6-git-send-email-namhyung@kernel.org


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