perf intel-pt: Add callchain to synthesized PEBS sample

Like other synthesized events, if there is also an Intel PT branch
trace, then a call stack can also be synthesized.  Add that.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/20190610072803.10456-12-adrian.hunter@intel.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>