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/stout_defconfig b/configs/stout_defconfig
index d353495..c5af189 100644
--- a/configs/stout_defconfig
+++ b/configs/stout_defconfig
@@ -20,3 +20,4 @@
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_BAR=y
 CONFIG_SPI_FLASH_SPANSION=y
+CONFIG_OF_LIBFDT=y