MN10300: Introduce a general config option for kernel debugger hooks

Introduce a general config option for kernel debugger hooks so that both
gdbstub and kgdb can use it and add a header file for both debuggers to use.

Signed-off-by: David Howells <dhowells@redhat.com>
diff --git a/arch/mn10300/Kconfig.debug b/arch/mn10300/Kconfig.debug
index a1b8620..87adb8f 100644
--- a/arch/mn10300/Kconfig.debug
+++ b/arch/mn10300/Kconfig.debug
@@ -150,3 +150,7 @@
 	default y
 
 endmenu
+
+config KERNEL_DEBUGGER
+	def_bool y
+	depends on GDBSTUB