perf build-id: Move build-id related functions to util/build-id.c

perf build-id: Move build-id related functions to util/build-id.c

It'd be better managing those functions in a separate place as
util/header.c file is already big.

It now exports following 3 functions to others:

  bool perf_session__read_build_ids(struct perf_session *session, bool with_hits);
  int perf_session__write_buildid_table(struct perf_session *session, int fd);
  int perf_session__cache_build_ids(struct perf_session *session);

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: http://lkml.kernel.org/r/545733E7.6010105@intel.com
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung.kim@lge.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1415063674-17206-5-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>