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/integratorcp_cm946es_defconfig b/configs/integratorcp_cm946es_defconfig
index a4aeba4..d4d11b8 100644
--- a/configs/integratorcp_cm946es_defconfig
+++ b/configs/integratorcp_cm946es_defconfig
@@ -4,3 +4,4 @@
 CONFIG_CM946ES=y
 CONFIG_SYS_PROMPT="Integrator-CP # "
 # CONFIG_CMD_SETEXPR is not set
+CONFIG_OF_LIBFDT=y