perf c2c: Introduce c2c_add_stats function

Introducing c2c_add_stats function helper to cumulate c2c_stats.

Original-patch-by: Dick Fowles <rfowles@redhat.com>
Original-patch-by: Don Zickus <dzickus@redhat.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Joe Mario <jmario@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1474558645-19956-4-git-send-email-jolsa@kernel.org


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