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/imx8mq-phanbell-u-boot.dtsi b/arch/arm/dts/imx8mq-phanbell-u-boot.dtsi
index 8d6f305..05f809c 100644
--- a/arch/arm/dts/imx8mq-phanbell-u-boot.dtsi
+++ b/arch/arm/dts/imx8mq-phanbell-u-boot.dtsi
@@ -7,9 +7,9 @@
 };
 
 &uart1 {
-	u-boot,dm-spl;
+	bootph-pre-ram;
 };
 
 &pinctrl_uart1 {
-	u-boot,dm-spl;
+	bootph-pre-ram;
 };