perf tools: Create config.detected into OUTPUT directory

Create config.detected into OUTPUT directory instead of source
directory.

This fixes parallel builds that share the same source directory.

Signed-off-by: Aaro Koskinen <aaro.koskinen@nokia.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1435751683-18500-1-git-send-email-aaro.koskinen@nokia.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>