dm: dts: Convert driver model tags to use new schema

Now that Linux has accepted these tags, move the device tree files in
U-Boot over to use them.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/dts/rk3568-evb-u-boot.dtsi b/arch/arm/dts/rk3568-evb-u-boot.dtsi
index 17503d3..382a52a 100644
--- a/arch/arm/dts/rk3568-evb-u-boot.dtsi
+++ b/arch/arm/dts/rk3568-evb-u-boot.dtsi
@@ -18,6 +18,6 @@
 
 &uart2 {
 	clock-frequency = <24000000>;
-	u-boot,dm-spl;
+	bootph-pre-ram;
 	status = "okay";
 };