MN10300: Create generic kernel debugger hooks

Create generic kernel debugger hooks in the MN10300 arch and make gdbstub use
them.  This is a preparation for KGDB support.

Signed-off-by: David Howells <dhowells@redhat.com>
diff --git a/arch/mn10300/include/asm/irqflags.h b/arch/mn10300/include/asm/irqflags.h
index 7a7ae12..678f68d 100644
--- a/arch/mn10300/include/asm/irqflags.h
+++ b/arch/mn10300/include/asm/irqflags.h
@@ -20,7 +20,7 @@
 /*
  * interrupt control
  * - "disabled": run in IM1/2
- *   - level 0 - GDB stub
+ *   - level 0 - kernel debugger
  *   - level 1 - virtual serial DMA (if present)
  *   - level 5 - normal interrupt priority
  *   - level 6 - timer interrupt