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/imx8mn-bsh-smm-s2-u-boot.dtsi b/arch/arm/dts/imx8mn-bsh-smm-s2-u-boot.dtsi
index bd4da7d..fb86657 100644
--- a/arch/arm/dts/imx8mn-bsh-smm-s2-u-boot.dtsi
+++ b/arch/arm/dts/imx8mn-bsh-smm-s2-u-boot.dtsi
@@ -7,9 +7,9 @@
 #include "imx8mn-bsh-smm-s2-u-boot-common.dtsi"
 
 &pinctrl_gpmi_nand {
-	u-boot,dm-spl;
+	bootph-pre-ram;
 };
 
 &gpmi {
-	u-boot,dm-spl;
+	bootph-pre-ram;
 };