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/armadillo-800eva_defconfig b/configs/armadillo-800eva_defconfig
index 240d72d..dc326e1 100644
--- a/configs/armadillo-800eva_defconfig
+++ b/configs/armadillo-800eva_defconfig
@@ -18,3 +18,4 @@
 # CONFIG_CMD_SOURCE is not set
 # CONFIG_CMD_SETEXPR is not set
 # CONFIG_CMD_MISC is not set
+CONFIG_OF_LIBFDT=y