dts: Disable device tree for SPL on all boards

We plan to enable device tree in SPL by default. Before doing this,
explicitly disable it for all boards.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/galileo_defconfig b/configs/galileo_defconfig
index a3b564e..5045510 100644
--- a/configs/galileo_defconfig
+++ b/configs/galileo_defconfig
@@ -5,5 +5,6 @@
 CONFIG_TARGET_GALILEO=y
 CONFIG_CMD_NET=y
 CONFIG_OF_CONTROL=y
+CONFIG_SPL_DISABLE_OF_CONTROL=y
 CONFIG_ETH_DESIGNWARE=y
 CONFIG_GENERATE_PIRQ_TABLE=y