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/bcm958300k_defconfig b/configs/bcm958300k_defconfig
index ba430e6..8fcde6c 100644
--- a/configs/bcm958300k_defconfig
+++ b/configs/bcm958300k_defconfig
@@ -5,3 +5,4 @@
 # CONFIG_CMD_FLASH is not set
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_SYS_NS16550=y
+CONFIG_OF_LIBFDT=y