image: Drop IMAGE_ENABLE_OF_LIBFDT

Add a host Kconfig for OF_LIBFDT. With this we can use
CONFIG_IS_ENABLED(OF_LIBFDT) directly in the tools build, so drop the
unnecessary indirection.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
diff --git a/common/image-board.c b/common/image-board.c
index 0ad75fd..cb2479f 100644
--- a/common/image-board.c
+++ b/common/image-board.c
@@ -282,7 +282,7 @@
 	if (image_check_magic(hdr))
 		return IMAGE_FORMAT_LEGACY;
 #endif
-#if CONFIG_IS_ENABLED(FIT) || IMAGE_ENABLE_OF_LIBFDT
+#if CONFIG_IS_ENABLED(FIT) || CONFIG_IS_ENABLED(OF_LIBFDT)
 	if (fdt_check_header(img_addr) == 0)
 		return IMAGE_FORMAT_FIT;
 #endif
@@ -895,7 +895,7 @@
 	struct lmb *lmb = &images->lmb;
 	int ret;
 
-	if (IMAGE_ENABLE_OF_LIBFDT)
+	if (CONFIG_IS_ENABLED(OF_LIBFDT))
 		boot_fdt_add_mem_rsv_regions(lmb, *of_flat_tree);
 
 	if (IMAGE_BOOT_GET_CMDLINE) {
@@ -907,13 +907,13 @@
 		}
 	}
 
-	if (IMAGE_ENABLE_OF_LIBFDT) {
+	if (CONFIG_IS_ENABLED(OF_LIBFDT)) {
 		ret = boot_relocate_fdt(lmb, of_flat_tree, &of_size);
 		if (ret)
 			return ret;
 	}
 
-	if (IMAGE_ENABLE_OF_LIBFDT && of_size) {
+	if (CONFIG_IS_ENABLED(OF_LIBFDT) && of_size) {
 		ret = image_setup_libfdt(images, *of_flat_tree, of_size, lmb);
 		if (ret)
 			return ret;