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/omap3_logic_defconfig b/configs/omap3_logic_defconfig
index 53c6913..a58b85a 100644
--- a/configs/omap3_logic_defconfig
+++ b/configs/omap3_logic_defconfig
@@ -11,3 +11,4 @@
 # CONFIG_CMD_FPGA is not set
 CONFIG_CMD_GPIO=y
 CONFIG_SYS_NS16550=y
+CONFIG_OF_LIBFDT=y