tools: fit_image: Add the loadable property to configs

When running mkimage with "-f auto", the loadable property
needs to be set in order to allow SPL FIT support to boot.

Signed-off-by: Abel Vesa <abel.vesa@nxp.com>
Tested-by: Fabio Estevam <festevam@gmail.com>
diff --git a/tools/fit_image.c b/tools/fit_image.c
index 4b62635..3b867e0 100644
--- a/tools/fit_image.c
+++ b/tools/fit_image.c
@@ -298,6 +298,7 @@
 		typename = genimg_get_type_short_name(params->fit_image_type);
 		snprintf(str, sizeof(str), "%s-1", typename);
 		fdt_property_string(fdt, typename, str);
+		fdt_property_string(fdt, FIT_LOADABLE_PROP, str);
 
 		if (params->fit_ramdisk)
 			fdt_property_string(fdt, FIT_RAMDISK_PROP,