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/hrcon_defconfig b/configs/hrcon_defconfig
index f6c531f..a4b733b 100644
--- a/configs/hrcon_defconfig
+++ b/configs/hrcon_defconfig
@@ -5,3 +5,4 @@
 CONFIG_AUTOBOOT_STOP_STR=" "
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_SYS_NS16550=y
+CONFIG_OF_LIBFDT=y