powerpc: MPC8536DS: Remove macro CONFIG_MPC8536DS

Use CONFIG_TARGET_MPC8536DS instead.

Signed-off-by: York Sun <york.sun@nxp.com>
diff --git a/board/freescale/common/pixis.h b/board/freescale/common/pixis.h
index 29a2eea..3c59157 100644
--- a/board/freescale/common/pixis.h
+++ b/board/freescale/common/pixis.h
@@ -7,7 +7,7 @@
 #define __PIXIS_H_	1
 
 /* PIXIS register set. */
-#if defined(CONFIG_MPC8536DS)
+#if defined(CONFIG_TARGET_MPC8536DS)
 typedef struct pixis {
 	u8 id;
 	u8 ver;