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/arch/arm/mach-imx/spl.c b/arch/arm/mach-imx/spl.c
index 30fa6ae..9fa397c 100644
--- a/arch/arm/mach-imx/spl.c
+++ b/arch/arm/mach-imx/spl.c
@@ -222,7 +222,7 @@
 }
 #endif
 
-#if defined(CONFIG_SECURE_BOOT)
+#if defined(CONFIG_IMX_HAB)
 
 /*
  * +------------+  0x0 (DDR_UIMAGE_START) -