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/smartweb_defconfig b/configs/smartweb_defconfig
index 654bb4b..1fd3e4d 100644
--- a/configs/smartweb_defconfig
+++ b/configs/smartweb_defconfig
@@ -7,3 +7,4 @@
 CONFIG_AUTOBOOT_KEYED=y
 CONFIG_AUTOBOOT_PROMPT="Autobooting in %d seconds, press \"<Esc><Esc>\" to stop\n"
 CONFIG_AUTOBOOT_STOP_STR="\x1b\x1b"
+CONFIG_OF_LIBFDT=y