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/gplugd_defconfig b/configs/gplugd_defconfig
index d2c5e6a..b7ef262 100644
--- a/configs/gplugd_defconfig
+++ b/configs/gplugd_defconfig
@@ -8,3 +8,4 @@
 CONFIG_SPI_FLASH_ATMEL=y
 CONFIG_SPI_FLASH_MACRONIX=y
 CONFIG_SYS_NS16550=y
+CONFIG_OF_LIBFDT=y