Now that we have the 'equal' method implemented for hpp format entries
we can ease up the logic in the following functions and make them
generic wrt comparing format entries:

  perf_hpp__setup_output_field
  perf_hpp__append_sort_keys
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/1453109064-1026-8-git-send-email-jolsa@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>