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/yosemite_defconfig b/configs/yosemite_defconfig
index cd852c2..9237996 100644
--- a/configs/yosemite_defconfig
+++ b/configs/yosemite_defconfig
@@ -3,3 +3,4 @@
 CONFIG_TARGET_YOSEMITE=y
 CONFIG_SYS_EXTRA_OPTIONS="YOSEMITE"
 CONFIG_SYS_NS16550=y
+CONFIG_OF_LIBFDT=y