perf tools: Add cpu to struct thread

Tools may wish to track on which cpu a thread is running.  Add 'cpu' to
struct thread for that purpose.

This will be used to determine the cpu when decoding a per-thread
Instruction Trace.

E.g: Intel PT decoding uses sched_switch events to determine which task
is running on which cpu.  The Intel PT data comes straight from the
hardware which doesn't know about linux threads.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1406035081-14301-16-git-send-email-adrian.hunter@intel.com


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