perf script: Allow time to be displayed in nanoseconds

Add option --ns to display time to 9 decimal places.  That is useful in
some cases, for example when using Intel PT cycle accurate mode.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/1443186956-18718-6-git-send-email-adrian.hunter@intel.com


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