perf session: Add instruction tracing options

It is assumed that AUX area decoding will synthesize events for
consumption by other tools.

At this time, the main use of AUX area tracing will be to capture
instruction trace (aka processor trace) data.

The nature of instruction tracing suggests the initial inclusion of
options for "instructions" and "branches" events, but more could be
added as needed.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.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/1428594864-29309-10-git-send-email-adrian.hunter@intel.com
[ Added ref to tools/perf/Documentation/perf-script.txt describing what is parsed ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>