imx: mx6slevk: Change to use generic board

Enable CONFIG_SYS_GENERIC_BOARD for imx6slevk to use generic board.
Signed-off-by: NYe.Li <B37916@freescale.com>

include/configs/mx6slevk.h

@@ -26,6 +26,8 @@
 #define CONFIG_INITRD_TAG
 #define CONFIG_REVISION_TAG
 
+#define CONFIG_SYS_GENERIC_BOARD
+
 /* Size of malloc() pool */
 #define CONFIG_SYS_MALLOC_LEN		(3 * SZ_1M)