mx31ads: Place machine ID into board config

Let common code set the machine ID.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
diff --git a/include/configs/mx31ads.h b/include/configs/mx31ads.h
index adb2ee1..0bea858 100644
--- a/include/configs/mx31ads.h
+++ b/include/configs/mx31ads.h
@@ -35,6 +35,8 @@
 
 #define CONFIG_SYS_TEXT_BASE		0xA0000000
 
+#define CONFIG_MACH_TYPE	MACH_TYPE_MX31ADS
+
 /*
  * Disabled for now due to build problems under Debian and a significant increase
  * in the final file size: 144260 vs. 109536 Bytes.