perf trace: Add an event duration column

perf trace: Add an event duration column

 # perf trace usleep 1 | tail -10
     0.453 ( 0.002 ms): mmap(addr: 0, len: 4096, prot: 3, flags: 34, fd: 4294967295, off: 0   ) = -763342848
     0.456 ( 0.001 ms): mmap(addr: 0, len: 4096, prot: 3, flags: 34, fd: 4294967295, off: 0   ) = -763346944
     0.459 ( 0.001 ms): arch_prctl(option: 4098, arg2: 140126839658240, arg3: 140126839652352, arg4: 34, arg5: 4294967295) = 0
     0.473 ( 0.003 ms): mprotect(start: 208741634048, len: 16384, prot: 1                     ) = 0
     0.477 ( 0.003 ms): mprotect(start: 208735956992, len: 4096, prot: 1                      ) = 0
     0.483 ( 0.004 ms): munmap(addr: 140126839664640, len: 91882                              ) = 0
     0.540 ( 0.001 ms): brk(brk: 0                                                            ) = 31928320
     0.542 ( 0.002 ms): brk(brk: 32063488                                                     ) = 32063488
     1.456 ( 0.901 ms): nanosleep(rqtp: 140735472817168, rmtp: 0                              ) = 0
     1.462 ( 0.000 ms): exit_group(error_code: 0
 #

This also comes from the tmp.perf/trace2 branch.

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/n/tip-g9akh5hjw2kvjerpo9xror6f@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>