mx7dsabresd: add secure boot support

Add secure boot support for mx7dsabresd target board

Signed-off-by: Adrian Alonso <aalonso@freescale.com>
diff --git a/board/freescale/mx7dsabresd/imximage.cfg b/board/freescale/mx7dsabresd/imximage.cfg
index 91b70ee..76574ff 100644
--- a/board/freescale/mx7dsabresd/imximage.cfg
+++ b/board/freescale/mx7dsabresd/imximage.cfg
@@ -23,6 +23,13 @@
 BOOT_FROM	sd
 
 /*
+ * Secure boot support
+ */
+#ifdef CONFIG_SECURE_BOOT
+CSF CONFIG_CSF_SIZE
+#endif
+
+/*
  * Device Configuration Data (DCD)
  *
  * Each entry must have the format: