perf tools: Output 'perf list' to stdout not stderr

Writing to stdout is probably the expected behavior because the
user explicitly asked for a list.

Signed-off-by: Marti Raudsepp <marti@juffo.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <4ebb59420ef057972167.1256603585@localhost>
Signed-off-by: Ingo Molnar <mingo@elte.hu>