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/ls2080a_simu_defconfig b/configs/ls2080a_simu_defconfig
index 4c19b89..fe8281b 100644
--- a/configs/ls2080a_simu_defconfig
+++ b/configs/ls2080a_simu_defconfig
@@ -14,3 +14,4 @@
 # CONFIG_CMD_MISC is not set
 CONFIG_NET_RANDOM_ETHADDR=y
 CONFIG_SYS_NS16550=y
+CONFIG_OF_LIBFDT=y