perfcounters fix section mismatch warning in perf_counter.c::perf_counters_lapic_init()

Fix:

WARNING: arch/x86/kernel/built-in.o(.text+0xdd0f): Section mismatch in reference from the function pmc_generic_enable() to the function .cpuinit.text:perf_counters_lapic_init()
The function pmc_generic_enable() references
the function __cpuinit perf_counters_lapic_init().
This is often because pmc_generic_enable lacks a __cpuinit
annotation or the annotation of perf_counters_lapic_init is wrong.

Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>