perf annotate: Support '--group' option

perf annotate: Support '--group' option

With the '--group' option, even for non-explicit group, 'perf annotate'
will enable the group output.

For example,

  $ perf record -e cycles,branches ./div
  $ perf annotate main --stdio --group

                 :            Disassembly of section .text:
                 :
                 :            00000000004004b0 <main>:
                 :            main():
                 :
                 :                    return i;
                 :            }
                 :
                 :            int main(void)
                 :            {
    0.00    0.00 :   4004b0:       push   %rbx
                 :                    int i;
                 :                    int flag;
                 :                    volatile double x = 1212121212, y = 121212;
                 :
                 :                    s_randseed = time(0);
    0.00    0.00 :   4004b1:       xor    %edi,%edi
                 :                    srand(s_randseed);
    0.00    0.00 :   4004b3:       mov    $0x77359400,%ebx
                 :
                 :                    return i;
                 :            }
                 :

But if without --group, there is only one event reported.

  $ perf annotate main --stdio

         :            Disassembly of section .text:
         :
         :            00000000004004b0 <main>:
         :            main():
         :
         :                    return i;
         :            }
         :
         :            int main(void)
         :            {
    0.00 :   4004b0:       push   %rbx
         :                    int i;
         :                    int flag;
         :                    volatile double x = 1212121212, y = 121212;
         :
         :                    s_randseed = time(0);
    0.00 :   4004b1:       xor    %edi,%edi
         :                    srand(s_randseed);
    0.00 :   4004b3:       mov    $0x77359400,%ebx
         :
         :                    return i;
         :            }

Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1526914666-31839-4-git-send-email-yao.jin@linux.intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>