x86: make nmi_shootdown_cpus() available on !SMP and !X86_LOCAL_APIC

Impact: widen nmi_shootdown_cpus() availability

The X86_LOCAL_APIC #ifdef was for kdump. For !SMP, the function simply
does nothing.
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/reboot.c

@@ -519,7 +519,7 @@ void machine_crash_shutdown(struct pt_regs *regs)
 #endif
 
 
-#if defined(CONFIG_SMP) && defined(CONFIG_X86_LOCAL_APIC)
+#if defined(CONFIG_SMP)
 
 /* This keeps a track of which one is crashing cpu. */
 static int crashing_cpu;
@@ -568,6 +568,12 @@ static struct notifier_block crash_nmi_nb = {
 	.notifier_call = crash_nmi_callback,
 };
 
+/* Halt all other CPUs, calling the specified function on each of them
+ *
+ * This function can be used to halt all other CPUs on crash
+ * or emergency reboot time. The function passed as parameter
+ * will be called inside a NMI handler on all CPUs.
+ */
 void nmi_shootdown_cpus(nmi_shootdown_cb callback)
 {
 	unsigned long msecs;
@@ -596,4 +602,9 @@ void nmi_shootdown_cpus(nmi_shootdown_cb callback)
 
 	/* Leave the nmi callback set */
 }
+#else /* !CONFIG_SMP */
+void nmi_shootdown_cpus(nmi_shootdown_cb callback)
+{
+	/* No other CPUs to shoot down */
+}
 #endif