kgdb: cpu/mpc* cpu/74xx: include kgdb.h when needed

Commit cbb0cab1d929839d broke some platforms which used kgdb code but
didn't actually include kgdb.h.  So include kgdb.h in all the relevant
traps code.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/cpu/mpc512x/traps.c b/cpu/mpc512x/traps.c
index 8000fab..786f4a5 100644
--- a/cpu/mpc512x/traps.c
+++ b/cpu/mpc512x/traps.c
@@ -28,6 +28,7 @@
  */
 
 #include <common.h>
+#include <kgdb.h>
 #include <asm/processor.h>
 
 DECLARE_GLOBAL_DATA_PTR;