[ppc] Fix build breakage for all non-4xx PowerPC variants.

- adapt to the more generic EXCEPTION_PROLOG and CRIT_EXCEPTION macros
- minor 4xx cleanup
diff --git a/include/mpc85xx.h b/include/mpc85xx.h
index a4d99b2..6fbd504 100644
--- a/include/mpc85xx.h
+++ b/include/mpc85xx.h
@@ -8,6 +8,7 @@
 #define __MPC85xx_H__
 
 #define EXC_OFF_SYS_RESET	0x0100	/* System reset	*/
+#define	_START_OFFSET		EXC_OFF_SYS_RESET
 
 #if defined(CONFIG_E500)
 #include <e500.h>