warp7: Switch to DM Serial

This commit switches to DM SERIAL for warp7 and warp7_bl33 defconfigs.

Signed-off-by: Pierre-Jean Texier <pjtexier@koncepto.io>
Signed-off-by: Joris Offouga <offougajoris@gmail.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
diff --git a/arch/arm/dts/imx7s-warp.dts b/arch/arm/dts/imx7s-warp.dts
index d28b7ec..4d87348 100644
--- a/arch/arm/dts/imx7s-warp.dts
+++ b/arch/arm/dts/imx7s-warp.dts
@@ -21,6 +21,10 @@
 		mmc0 = &usdhc3;
 	};
 
+	chosen {
+		stdout-path = &uart1;
+	};
+
 	gpio-keys {
 		compatible = "gpio-keys";
 		pinctrl-0 = <&pinctrl_gpio>;