[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/mpc8260.h b/include/mpc8260.h
index d9dd92d..b61218c 100644
--- a/include/mpc8260.h
+++ b/include/mpc8260.h
@@ -53,7 +53,7 @@
  * Exception offsets (PowerPC standard)
  */
 #define EXC_OFF_SYS_RESET	0x0100	/* System reset			*/
-
+#define _START_OFFSET		EXC_OFF_SYS_RESET
 
 /*-----------------------------------------------------------------------
  * BCR - Bus Configuration Register					 4-25