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/PMC405DE_defconfig b/configs/PMC405DE_defconfig
index 53fccf5..fc78a64 100644
--- a/configs/PMC405DE_defconfig
+++ b/configs/PMC405DE_defconfig
@@ -6,3 +6,4 @@
 CONFIG_AUTOBOOT_STOP_STR=" "
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_SYS_NS16550=y
+CONFIG_OF_LIBFDT=y