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/kwb_defconfig b/configs/kwb_defconfig
index 4d2aa6c..ce66f76 100644
--- a/configs/kwb_defconfig
+++ b/configs/kwb_defconfig
@@ -26,6 +26,7 @@
 CONFIG_CMD_TIME=y
 CONFIG_NETCONSOLE=y
 CONFIG_SYS_NS16550=y
+CONFIG_OF_LIBFDT=y
 CONFIG_USB=y
 CONFIG_USB_MUSB_HOST=y
 CONFIG_USB_STORAGE=y