perf c2c report: Add sample processing

Adding basic sample processing specific hist_entry allocation callbacks
(via hists__add_entry_ops).

Overloading 'struct hist_entry' object with new 'struct c2c_hist_entry'.
The new hist entry object will carry specific stats and nested hists
objects.

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/1474558645-19956-17-git-send-email-jolsa@kernel.org


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