perf trace: Add summary option to dump syscall statistics

perf trace: Add summary option to dump syscall statistics

When enabled dumps a summary of all syscalls by task with the usual
statistics -- min, max, average and relative stddev. For example,

make - 26341 :       3344   [ 17.4% ]      0.000 ms

                read :   52    0.000     4.802     0.644   30.08
               write :   20    0.004     0.036     0.010   21.72
                open :   24    0.003     0.046     0.014   23.68
               close :   64    0.002     0.055     0.008   22.53
                stat : 2714    0.002     0.222     0.004    4.47
               fstat :   18    0.001     0.041     0.006   46.26
                mmap :   30    0.003     0.009     0.006    5.71
            mprotect :    8    0.006     0.039     0.016   32.16
              munmap :   12    0.007     0.077     0.020   38.25
                 brk :   48    0.002     0.014     0.004   10.18
        rt_sigaction :   18    0.002     0.002     0.002    2.11
      rt_sigprocmask :   60    0.002     0.128     0.010   32.88
              access :    2    0.006     0.006     0.006    0.00
                pipe :   12    0.004     0.048     0.013   35.98
               vfork :   34    0.448     0.980     0.692    3.04
              execve :   20    0.000     0.387     0.046   56.66
               wait4 :   34    0.017  9923.287   593.221   68.45
               fcntl :    8    0.001     0.041     0.013   48.79
            getdents :   48    0.002     0.079     0.013   19.62
              getcwd :    2    0.005     0.005     0.005    0.00
               chdir :    2    0.070     0.070     0.070    0.00
           getrlimit :    2    0.045     0.045     0.045    0.00
          arch_prctl :    2    0.002     0.002     0.002    0.00
           setrlimit :    2    0.002     0.002     0.002    0.00
              openat :   94    0.003     0.005     0.003    2.11

Signed-off-by: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung.kim@lge.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1381289214-24885-3-git-send-email-dsahern@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>