x86: move prefill_possible_map to common file

this patches moves prefill_possible_map() to smpboot.c
Right now it is x86_64-specific, but nothing intrinsically
prevents it to be used by i386

Signed-off-by: Glauber Costa <gcosta@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/asm-x86/smp.h b/include/asm-x86/smp.h
index be8a511..28cb1f8 100644
--- a/include/asm-x86/smp.h
+++ b/include/asm-x86/smp.h
@@ -63,6 +63,7 @@
 int native_cpu_up(unsigned int cpunum);
 
 extern unsigned disabled_cpus;
+extern void prefill_possible_map(void);
 #endif
 
 #ifdef CONFIG_X86_32
diff --git a/include/asm-x86/smp_64.h b/include/asm-x86/smp_64.h
index c7a00ca..e5bc1be 100644
--- a/include/asm-x86/smp_64.h
+++ b/include/asm-x86/smp_64.h
@@ -43,7 +43,6 @@
 
 extern int __cpu_disable(void);
 extern void __cpu_die(unsigned int cpu);
-extern void prefill_possible_map(void);
 
 #define raw_smp_processor_id()	read_pda(cpunumber)
 #define cpu_physical_id(cpu)	per_cpu(x86_cpu_to_apicid, cpu)