perf evsel: Introduce perf_evsel__is_group_event() helper

perf evsel: Introduce perf_evsel__is_group_event() helper

The perf_evsel__is_group_event function is for checking whether given
evsel needs event group view support or not.  Please note that it's
different to the existing perf_evsel__is_group_leader() which checks
only the given evsel is a leader or a standalone (i.e. non-group) event
regardless of event group feature.

Signed-off-by: Namhyung Kim <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>