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/kmopti2_defconfig b/configs/kmopti2_defconfig
index 6d7896e..798f748 100644
--- a/configs/kmopti2_defconfig
+++ b/configs/kmopti2_defconfig
@@ -3,3 +3,4 @@
 CONFIG_TARGET_TUXX1=y
 CONFIG_SYS_EXTRA_OPTIONS="KMOPTI2"
 CONFIG_SYS_NS16550=y
+CONFIG_OF_LIBFDT=y