image: fix compiling without CMD_FDT

Booting an image currently sets the environment variable "fdtaddr"
by calling into 'cmd/fdt.c'. As a result, linking U-Boot fails if
CMD_FDT is not enabled.

Fix this by adding 'if (CONFIG_IS_ENABLED(CMD_FDT))' to the two
places where 'set_working_fdt_addr()' is called.

Signed-off-by: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>
diff --git a/common/bootm.c b/common/bootm.c
index 8bf84eb..80f304c 100644
--- a/common/bootm.c
+++ b/common/bootm.c
@@ -262,7 +262,8 @@
 		puts("Could not find a valid device tree\n");
 		return 1;
 	}
-	set_working_fdt_addr(map_to_sysmem(images.ft_addr));
+	if (CONFIG_IS_ENABLED(CMD_FDT))
+		set_working_fdt_addr(map_to_sysmem(images.ft_addr));
 #endif
 
 #if IMAGE_ENABLE_FIT
diff --git a/common/image-fdt.c b/common/image-fdt.c
index 95748f0..8ee5a13 100644
--- a/common/image-fdt.c
+++ b/common/image-fdt.c
@@ -193,7 +193,8 @@
 	*of_flat_tree = of_start;
 	*of_size = of_len;
 
-	set_working_fdt_addr(map_to_sysmem(*of_flat_tree));
+	if (CONFIG_IS_ENABLED(CMD_FDT))
+		set_working_fdt_addr(map_to_sysmem(*of_flat_tree));
 	return 0;
 
 error: