x86: Drop rtc from SPL

The RTC is not currently used in SPL. Drop it so that it does not take up
space.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/x86/dts/rtc.dtsi b/arch/x86/dts/rtc.dtsi
index d0bbd84..942cc93 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-reloc;
+		u-boot,dm-pre-proper;
 		reg = <0x70 2>;
 	};
 };