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/ls1021atwr_nor_SECURE_BOOT_defconfig b/configs/ls1021atwr_nor_SECURE_BOOT_defconfig
index 2533cdd..07b3c81 100644
--- a/configs/ls1021atwr_nor_SECURE_BOOT_defconfig
+++ b/configs/ls1021atwr_nor_SECURE_BOOT_defconfig
@@ -7,3 +7,4 @@
 CONFIG_NETDEVICES=y
 CONFIG_E1000=y
 CONFIG_SYS_NS16550=y
+CONFIG_OF_LIBFDT=y