imx: replace CONFIG_SECURE_BOOT with CONFIG_IMX_HAB

CONFIG_SECURE_BOOT is too generic and forbids to use it for cross
architecture purposes. If Secure Boot is required for imx, this means to
enable and use the HAB processor in the soc.

Signed-off-by: Stefano Babic <sbabic@denx.de>
diff --git a/board/boundary/nitrogen6x/nitrogen6dl.cfg b/board/boundary/nitrogen6x/nitrogen6dl.cfg
index b1e3c0f..56b3bcb 100644
--- a/board/boundary/nitrogen6x/nitrogen6dl.cfg
+++ b/board/boundary/nitrogen6x/nitrogen6dl.cfg
@@ -19,7 +19,7 @@
 
 #define __ASSEMBLY__
 #include <config.h>
-#ifdef CONFIG_SECURE_BOOT
+#ifdef CONFIG_IMX_HAB
 CSF CONFIG_CSF_SIZE
 #endif
 #include "asm/arch/mx6-ddr.h"