perf_counter: PERF_TYPE_HW_CACHE is a hardware counter too

is_software_counter() was missing the new HW_CACHE category.

( This could have caused some counter scheduling artifacts
  with mixed sw and hw counters and counter groups. )

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>