dts: xea: Enable debug UART support in XEA's SPL (DM_SERIAL)

After enabling DM_SERIAL for XEA board, the same serial shall be used
in the SPL (with SPL_OF_PLATDATA support).

Signed-off-by: Lukasz Majewski <lukma@denx.de>
diff --git a/arch/arm/dts/imx28-xea-u-boot.dtsi b/arch/arm/dts/imx28-xea-u-boot.dtsi
index 9f1e261..e40a6d2 100644
--- a/arch/arm/dts/imx28-xea-u-boot.dtsi
+++ b/arch/arm/dts/imx28-xea-u-boot.dtsi
@@ -34,6 +34,10 @@
 	bootph-pre-ram;
 };
 
+&duart {
+	bootph-pre-ram;
+};
+
 &gpio0 {
 	bootph-pre-ram;
 };