powerpc: mpc5xxx: remove redundant CONFIG_MPC5xxx definition

We do not have to define CONFIG_MPC5xxx in board config headers
(and start.S) because it is defined in arch/powerpc/cpu/mpc5xxx/config.mk.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/include/configs/PM520.h b/include/configs/PM520.h
index 557a8ba..de46216 100644
--- a/include/configs/PM520.h
+++ b/include/configs/PM520.h
@@ -14,8 +14,7 @@
  */
 
 #define CONFIG_MPC5200
-#define CONFIG_MPC5xxx		1	/* This is an MPC5xxx CPU */
-#define CONFIG_PM520		1	/* ... on PM520 board */
+#define CONFIG_PM520		1	/* PM520 board */
 
 #define	CONFIG_SYS_TEXT_BASE	0xfff00000