perf/x86: Convert obsolete simple_strtoul() usage to kstrtoul()

Signed-off-by: Shuah Khan <shuahkhan@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Link: http://lkml.kernel.org/r/1339384421.3025.8.camel@lorien2
Signed-off-by: Ingo Molnar <mingo@kernel.org>