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/gdppc440etx_defconfig b/configs/gdppc440etx_defconfig
index 9b06cb6..0c04678 100644
--- a/configs/gdppc440etx_defconfig
+++ b/configs/gdppc440etx_defconfig
@@ -4,3 +4,4 @@
 CONFIG_AUTOBOOT_KEYED=y
 CONFIG_AUTOBOOT_STOP_STR=" "
 CONFIG_SYS_NS16550=y
+CONFIG_OF_LIBFDT=y