x86, smp: refactor ->smp_callin_clear_local_apic() methods

Only NUMAQ does something substantial here, because it initializes
via NMIs (not via INIT as standard SMP startup) - so it needs to
reset the APIC.

 - extend the generic code to handle NULL methods

 - clear out dummy methods and replace them with NULL

 - clean up: remove wrapper macros, etc.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 558af37..10873a4 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -244,7 +244,8 @@
 	 */
 
 	pr_debug("CALLIN, before setup_local_APIC().\n");
-	smp_callin_clear_local_apic();
+	if (apic->smp_callin_clear_local_apic)
+		apic->smp_callin_clear_local_apic();
 	setup_local_APIC();
 	end_local_APIC_setup();
 	map_cpu_to_logical_apicid();