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_cm926ejs_defconfig b/configs/integratorap_cm926ejs_defconfig
index cf75425..f58e256 100644
--- a/configs/integratorap_cm926ejs_defconfig
+++ b/configs/integratorap_cm926ejs_defconfig
@@ -4,3 +4,4 @@
 CONFIG_CM926EJ_S=y
 CONFIG_SYS_PROMPT="Integrator-AP # "
 # CONFIG_CMD_SETEXPR is not set
+CONFIG_OF_LIBFDT=y