rockchip: rk322x: dts: enable uart2 for SPL/TPL

When we use DM_SERIAL for serial driver, we need enable the
dts node for the debug console.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/arch/arm/dts/rk3229-evb.dts b/arch/arm/dts/rk3229-evb.dts
index bfb367a..632cdc9 100644
--- a/arch/arm/dts/rk3229-evb.dts
+++ b/arch/arm/dts/rk3229-evb.dts
@@ -82,6 +82,7 @@
 };
 
 &uart2 {
+	u-boot,dm-pre-reloc;
 	status = "okay";
 };