rockchip: dts: rk3399-puma: make the debug serial dm-pre-reloc

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

arch/arm/dts/rk3399-puma.dts

@@ -107,6 +107,7 @@
 };
 
 &uart0 {
+	u-boot,dm-pre-reloc;
 	status = "okay";
 };