perf tools: Add Intel PT log

Add a facility to log Intel Processor Trace decoding.  The log is
intended for debugging purposes only.

The log file name is "intel_pt.log" and is opened in the current
directory.  The log contains a record of all packets and instructions
decoded and can get very large (10 MB would be a small one).

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/1437150840-31811-5-git-send-email-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>