perf_counter: Change PERF_SAMPLE_CONFIG into PERF_SAMPLE_ID

The purpose of PERF_SAMPLE_CONFIG was to identify the counters,
since then we've added counter ids, use those instead.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>