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/sbc8349_PCI_33_defconfig b/configs/sbc8349_PCI_33_defconfig
index 068b1b6..f78d205 100644
--- a/configs/sbc8349_PCI_33_defconfig
+++ b/configs/sbc8349_PCI_33_defconfig
@@ -4,3 +4,4 @@
 CONFIG_SYS_EXTRA_OPTIONS="PCI,PCI_33M"
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_SYS_NS16550=y
+CONFIG_OF_LIBFDT=y