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/hikey_defconfig b/configs/hikey_defconfig
index fd94bf5..8b75642 100644
--- a/configs/hikey_defconfig
+++ b/configs/hikey_defconfig
@@ -2,3 +2,4 @@
 CONFIG_SYS_MALLOC_F_LEN=0x2000
 # CONFIG_CMD_IMLS is not set
 CONFIG_CMD_GPIO=y
+CONFIG_OF_LIBFDT=y