perf tools: Enable event_config terms to tracepoint events

This patch enables config terms for tracepoint perf events. Valid terms
for tracepoint events are 'call-graph' and 'stack-size', so we can use
different callgraph settings for each event and eliminate unnecessary
overhead.

Here is an example for using different call-graph config for each
tracepoint.

  $ perf record -e syscalls:sys_enter_write/call-graph=fp/
                -e syscalls:sys_exit_write/call-graph=no/
                dd if=/dev/zero of=test bs=4k count=10

  $ perf report --stdio

  #
  # Total Lost Samples: 0
  #
  # Samples: 13  of event 'syscalls:sys_enter_write'
  # Event count (approx.): 13
  #
  # Children      Self  Command  Shared Object       Symbol
  # ........  ........  .......  ..................  ......................
  #
      76.92%    76.92%  dd       libpthread-2.20.so  [.] __write_nocancel
                   |
                   ---__write_nocancel

      23.08%    23.08%  dd       libc-2.20.so        [.] write
                   |
                   ---write
                      |
                      |--33.33%-- 0x2031342820736574
                      |
                      |--33.33%-- 0xa6e69207364726f
                      |
                       --33.33%-- 0x34202c7320393039
  ...

  # Samples: 13  of event 'syscalls:sys_exit_write'
  # Event count (approx.): 13
  #
  # Children      Self  Command  Shared Object       Symbol
  # ........  ........  .......  ..................  ......................
  #
      76.92%    76.92%  dd       libpthread-2.20.so  [.] __write_nocancel
      23.08%    23.08%  dd       libc-2.20.so        [.] write
       7.69%     0.00%  dd       [unknown]           [.] 0x0a6e69207364726f
       7.69%     0.00%  dd       [unknown]           [.] 0x2031342820736574
       7.69%     0.00%  dd       [unknown]           [.] 0x34202c7320393039

Signed-off-by: He Kuang <hekuang@huawei.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Wang Nan <wangnan0@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1443412336-120050-4-git-send-email-hekuang@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>