mx6slevk: imximage.cfg: Handle the CONFIG_SECURE_BOOT case

Secure boot is not enabled in mx6slevk imximage.cfg, add support for it.
Signed-off-by: NBreno Lima <breno.lima@nxp.com>
Reviewed-by: NFabio Estevam <fabio.estevam@nxp.com>
Acked-by: NPeng Fan <peng.fan@nxp.com>

board/freescale/mx6slevk/imximage.cfg

@@ -8,6 +8,8 @@
  *
  * The syntax is taken as close as possible with the kwbimage
  */
+#define __ASSEMBLY__
+#include <config.h>
 
 /* image version */
 
@@ -20,6 +22,13 @@ IMAGE_VERSION 2
 
 BOOT_FROM	sd
 
+/*
+ * Secure boot support
+ */
+#ifdef CONFIG_SECURE_BOOT
+CSF CONFIG_CSF_SIZE
+#endif
+
 /*
  * Device Configuration Data (DCD)
  *