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/picosam9g45_defconfig b/configs/picosam9g45_defconfig
index ccca1ca..687e69b 100644
--- a/configs/picosam9g45_defconfig
+++ b/configs/picosam9g45_defconfig
@@ -11,3 +11,4 @@
 # CONFIG_CMD_FLASH is not set
 # CONFIG_CMD_FPGA is not set
 # CONFIG_CMD_SETEXPR is not set
+CONFIG_OF_LIBFDT=y