Add an index of AUX area tracing events within a perf.data file.

perf record uses a special user event PERF_RECORD_FINISHED_ROUND to
enable sorting of events in chunks instead of having to sort all events
altogether.

AUX area tracing events contain data that can span back to the very
beginning of the recording period. i.e. they do not obey the rules of
PERF_RECORD_FINISHED_ROUND.

By adding an index, AUX area tracing events can be found in advance and
the PERF_RECORD_FINISHED_ROUND approach works as usual.

The index is recorded with the auxtrace feature in the perf.data file.
A session reads the index but does not process it.  An AUX area decoder
can queue all the AUX area data in advance using
auxtrace_queues__process_index() or otherwise process the index in some
custom manner.
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1430404667-10593-3-git-send-email-adrian.hunter@intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>