imx: imx8mq-evk: enable CONFIG_DM_SERIAL

Marked related nodes as u-boot,dm-spl for serial driver model
Enable CONFIG_DM_SERIAL

Signed-off-by: Peng Fan <peng.fan@nxp.com>

arch/arm/dts/imx8mq-evk-u-boot.dtsi

@@ -2,6 +2,34 @@
 
 #include "imx8mq-u-boot.dtsi"
 
+&{/soc@0} {
+	u-boot,dm-spl;
+};
+
+&{/soc@0/bus@30000000} {
+	u-boot,dm-spl;
+};
+
+&{/soc@0/bus@30400000} {
+	u-boot,dm-spl;
+};
+
+&{/soc@0/bus@30800000} {
+	u-boot,dm-spl;
+};
+
+&{/soc@0/bus@32c00000} {
+	u-boot,dm-spl;
+};
+
+&iomuxc {
+	u-boot,dm-spl;
+};
+
+&pinctrl_uart1 {
+	u-boot,dm-spl;
+};
+
 &usdhc1 {
 	mmc-hs400-1_8v;
 };
@@ -10,3 +38,7 @@
 	sd-uhs-sdr104;
 	sd-uhs-ddr50;
 };
+
+&uart1 {
+	u-boot,dm-spl;
+};