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/fo300_defconfig b/configs/fo300_defconfig
index b8e5c80..9a857b6 100644
--- a/configs/fo300_defconfig
+++ b/configs/fo300_defconfig
@@ -3,3 +3,4 @@
 CONFIG_TARGET_TQM5200=y
 CONFIG_SYS_EXTRA_OPTIONS="FO300"
 # CONFIG_CMD_SETEXPR is not set
+CONFIG_OF_LIBFDT=y