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/MPC8349ITX_LOWBOOT_defconfig b/configs/MPC8349ITX_LOWBOOT_defconfig
index c260a46..9b85433 100644
--- a/configs/MPC8349ITX_LOWBOOT_defconfig
+++ b/configs/MPC8349ITX_LOWBOOT_defconfig
@@ -5,3 +5,4 @@
 CONFIG_SYS_PROMPT="MPC8349E-mITX> "
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_SYS_NS16550=y
+CONFIG_OF_LIBFDT=y