perf tools: Add support for PERF_RECORD_ITRACE_START

Add support for the PERF_RECORD_ITRACE_START event type.  This event can
be used to determine the pid and tid that are running when Instruction
Tracing starts.  Generally that information would come from a
sched_switch event but, at the start, no sched_switch events may yet
have been recorded.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.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/1430404667-10593-8-git-send-email-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>