x86, smp: refactor ->store/restore_NMI_vector() methods

Only NUMAQ does something substantial here, because it initializes
via NMIs (not via INIT as standard SMP startup) - so it needs to
store and restore the NMI vector.

 - 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>

arch/x86/kernel/smpboot.c

@@ -826,7 +826,8 @@ do_rest:
 
 		pr_debug("Setting warm reset code and vector.\n");
 
-		store_NMI_vector(&nmi_high, &nmi_low);
+		if (apic->store_NMI_vector)
+			apic->store_NMI_vector(&nmi_high, &nmi_low);
 
 		smpboot_setup_warm_reset_vector(start_ip);
 		/*