[MIPS] kgdb: add arch support for the kernel's kgdb core

The new kgdb architecture specific handler registers and unregisters
dynamically for exceptions depending on when you configure a kgdb I/O
driver.

Aside from initializing the exceptions earlier in the boot process,
kgdb should have no impact on a device when it is compiled in so long
as an I/O module is not configured for use.

There have been quite a number of contributors during the existence of
this patch (see arch/mips/kernel/kgdb.c).  Most recently Jason
re-wrote the mips kgdb logic to use the die notification handlers.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/irq.c

@@ -21,11 +21,16 @@
 #include <linux/sched.h>
 #include <linux/seq_file.h>
 #include <linux/kallsyms.h>
+#include <linux/kgdb.h>
 
 #include <asm/atomic.h>
 #include <asm/system.h>
 #include <asm/uaccess.h>
 
+#ifdef CONFIG_KGDB
+int kgdb_early_setup;
+#endif
+
 static unsigned long irq_map[NR_IRQS / BITS_PER_LONG];
 
 int allocate_irqno(void)
@@ -130,8 +135,18 @@ void __init init_IRQ(void)
 {
 	int i;
 
+#ifdef CONFIG_KGDB
+	if (kgdb_early_setup)
+		return;
+#endif
+
 	for (i = 0; i < NR_IRQS; i++)
 		set_irq_noprobe(i);
 
 	arch_init_irq();
+
+#ifdef CONFIG_KGDB
+	if (!kgdb_early_setup)
+		kgdb_early_setup = 1;
+#endif
 }