perf script: Add call path id to exported sample in db export

perf script: Add call path id to exported sample in db export

The exported sample now contains a reference to the call_path_id that
represents its callchain.

While callchains themselves are nice to have, being able to associate
them with samples makes them much more useful, and can allow for such
things as determining how much cumulative time is spent in a particular
function. This information is normally possible to get from the call
return processor. However, when doing normal sampling, call/return
information is not available, thus necessitating the need for
associating samples directly with call paths.

This commit include changes to db-export layer to make this information
available for subsequent patches in this change set, but by itself, does
not make any changes visible to the user.

Signed-off-by: Chris Phlipot <cphlipot0@gmail.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1461831551-12213-5-git-send-email-cphlipot0@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>