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/x86/dts/rtc.dtsi b/arch/x86/dts/rtc.dtsi
index 942cc93..1c2eb28 100644
--- a/arch/x86/dts/rtc.dtsi
+++ b/arch/x86/dts/rtc.dtsi
@@ -1,7 +1,7 @@
 / {
 	rtc: rtc {
 		compatible = "motorola,mc146818";
-		u-boot,dm-pre-proper;
+		bootph-some-ram;
 		reg = <0x70 2>;
 	};
 };