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/MPC8349ITXGP_defconfig b/configs/MPC8349ITXGP_defconfig
index 445beb6..c1bc8ca 100644
--- a/configs/MPC8349ITXGP_defconfig
+++ b/configs/MPC8349ITXGP_defconfig
@@ -5,3 +5,4 @@
 CONFIG_SYS_PROMPT="MPC8349E-mITX-GP> "
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_SYS_NS16550=y
+CONFIG_OF_LIBFDT=y