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/integratorap_cm720t_defconfig b/configs/integratorap_cm720t_defconfig
index 5541f8e..6291139 100644
--- a/configs/integratorap_cm720t_defconfig
+++ b/configs/integratorap_cm720t_defconfig
@@ -4,3 +4,4 @@
 CONFIG_CM720T=y
 CONFIG_SYS_PROMPT="Integrator-AP # "
 # CONFIG_CMD_SETEXPR is not set
+CONFIG_OF_LIBFDT=y