perf, x86: Use ALTERNATIVE() to check for X86_FEATURE_PERFCTR_CORE

Using ALTERNATIVE() when checking for X86_FEATURE_PERFCTR_CORE avoids
an extra pointer chase and data cache hit.

Signed-off-by: Robert Richter <robert.richter@amd.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1302913676-14352-4-git-send-email-robert.richter@amd.com


Signed-off-by: Ingo Molnar <mingo@elte.hu>