perf hists: Add perf_hpp_list register helpers

Adding 2 perf_hpp_list register helpers:

  perf_hpp_list__column_register()
  perf_hpp_list__register_sort_field()

to be called within existing helpers:

  perf_hpp__column_register()
  perf_hpp__register_sort_field()

to register format entries within global perf_hpp_list object.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1453109064-1026-17-git-send-email-jolsa@kernel.org


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