MX5: rename mx51 to mx5

Rename mx51 to mx5 in order to support more mx51
like-style SOCs such as MX53 and the followings.

Signed-off-by: Jason Liu <r64343@freescale.com>
diff --git a/include/configs/vision2.h b/include/configs/vision2.h
index 44a6f8b..a2ecbe5 100644
--- a/include/configs/vision2.h
+++ b/include/configs/vision2.h
@@ -29,8 +29,8 @@
 #define CONFIG_MX51	/* in a mx51 */
 #define CONFIG_L2_OFF
 
-#define CONFIG_MX51_HCLK_FREQ		24000000
-#define CONFIG_MX51_CLK32		32768
+#define CONFIG_SYS_MX5_HCLK	24000000
+#define CONFIG_SYS_MX5_CLK32		32768
 #define CONFIG_DISPLAY_CPUINFO
 #define CONFIG_DISPLAY_BOARDINFO