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/mpc8260/traps.c b/cpu/mpc8260/traps.c
index f9f4dea..d216f71 100644
--- a/cpu/mpc8260/traps.c
+++ b/cpu/mpc8260/traps.c
@@ -34,6 +34,7 @@
 
 #include <common.h>
 #include <command.h>
+#include <kgdb.h>
 #include <asm/processor.h>
 #include <asm/m8260_pci.h>