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/rut_defconfig b/configs/rut_defconfig
index 4c1fd4b..647088e 100644
--- a/configs/rut_defconfig
+++ b/configs/rut_defconfig
@@ -12,3 +12,4 @@
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_WINBOND=y
 CONFIG_SYS_NS16550=y
+CONFIG_OF_LIBFDT=y