perf scripts python: intel-pt-events.py: Add branches to script

As an example, add branch information to intel-pt-events.py script.
This shows how a simple python script can be used to customize
perf script output for Intel PT branch traces or power event traces.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: https://lore.kernel.org/r/20210525095112.1399-11-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>