libfdt: Conditionally compile based on CONFIG_OF_LIBFDT

This is the way u-boot reduces configured-out code.  At Wolfgang
Grandegger and Wolfgang Denk's request, make libfdt conform.

Signed-off-by: Gerald Van Baren <vanbaren@cideas.com>
diff --git a/libfdt/fdt_strerror.c b/libfdt/fdt_strerror.c
index 7f231ce..b49c952 100644
--- a/libfdt/fdt_strerror.c
+++ b/libfdt/fdt_strerror.c
@@ -16,6 +16,9 @@
  * License along with this library; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
  */
+#include "config.h"
+#if CONFIG_OF_LIBFDT
+
 #include "libfdt_env.h"
 
 #include <fdt.h>
@@ -62,3 +65,5 @@
 
 	return "<unknown error>";
 }
+
+#endif /* CONFIG_OF_LIBFDT */