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/novena_defconfig b/configs/novena_defconfig
index 889aac2..148d693 100644
--- a/configs/novena_defconfig
+++ b/configs/novena_defconfig
@@ -6,3 +6,4 @@
 # CONFIG_CMD_IMLS is not set
 # CONFIG_CMD_FLASH is not set
 CONFIG_CMD_GPIO=y
+CONFIG_OF_LIBFDT=y