Move CONFIG_OF_LIBFDT to Kconfig

Move this option to Kconfig and tidy up existing boards.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/udoo_defconfig b/configs/udoo_defconfig
index 0a7f70a..3f53749 100644
--- a/configs/udoo_defconfig
+++ b/configs/udoo_defconfig
@@ -6,3 +6,4 @@
 CONFIG_CMD_GPIO=y
 CONFIG_DM=y
 CONFIG_DM_THERMAL=y
+CONFIG_OF_LIBFDT=y