[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/mpc8220.h b/include/mpc8220.h
index ff7acc6..d3b1457 100644
--- a/include/mpc8220.h
+++ b/include/mpc8220.h
@@ -35,6 +35,7 @@
 
 /* Exception offsets (PowerPC standard) */
 #define EXC_OFF_SYS_RESET   0x0100
+#define _START_OFFSET	EXC_OFF_SYS_RESET
 
 /* Internal memory map */
 /* MPC8220 Internal Register MMAP */