[AVR32] NMI debugging

Change the NMI handler to use the die notifier chain to signal anyone
who cares. Add a simple "nmi debugger" which hooks into this chain and
that may dump registers, task state, etc. when it happens.

Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>

arch/avr32/kernel/irq.c

@@ -25,6 +25,17 @@ void ack_bad_irq(unsigned int irq)
 	printk("unexpected IRQ %u\n", irq);
 }
 
+/* May be overridden by platform code */
+int __weak nmi_enable(void)
+{
+	return -ENOSYS;
+}
+
+void __weak nmi_disable(void)
+{
+
+}
+
 #ifdef CONFIG_PROC_FS
 int show_interrupts(struct seq_file *p, void *v)
 {