This is needed, so far, just in 'perf stat', to scale counters, so don't
unconditionally ask for them in the perf_evsel__config() method.

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
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/n/tip-ujpujgscq2f2oodxuso5nobc@git.kernel.orgSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>