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/mgcoge_defconfig b/configs/mgcoge_defconfig
index 1fb8dfd..8c57b6c 100644
--- a/configs/mgcoge_defconfig
+++ b/configs/mgcoge_defconfig
@@ -2,3 +2,4 @@
 CONFIG_MPC8260=y
 CONFIG_TARGET_KM82XX=y
 CONFIG_SYS_EXTRA_OPTIONS="MGCOGE"
+CONFIG_OF_LIBFDT=y