perf report: Change default to use event group view

The event group view feature is to see related events together.  To use
the group view, events should be recorded as a group with a dedicated
syntax of surrounding events by braces (-e '{ evt1, evt2, ... }').

Also 'perf report' also requires the --group option to enable it.
However it's almost always beneficial to use the group view to see the
group events as it's more expressive.  And I think it's more natural to
see events together if they are recorded as a group.

Thus this patch changes the default value to enable it.  If users don't
want to see like it and keep the original behavior, they can set the
report.group config variable to false and/or use --no-group option in
the 'perf report' command line.

Requested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Cc: Taeung Song <treeze.taeung@gmail.com>
Link: http://lkml.kernel.org/r/1448807057-3506-1-git-send-email-namhyung@kernel.org


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