arm64:dts:imx8mp-d18: Fix FNG-System boot

Add aliases for serial interfaces and rtcs.
Disable flexspi node for now, because FNG-System stucks during
boot when it is enabled.

BCS 746-001343

arch/arm64/boot/dts/seco/imx8mp-d18.dtsi

@@ -14,6 +14,14 @@ / {
 	model = "SECO i.MX8MPlus LPDDR4 D18 board";
 	compatible = "fsl,imx8mp-evk", "seco,imx8mp-d18", "fsl,imx8mp";
 
+	aliases {
+		rtc0 = &rtc;
+		rtc1 = &snvs_rtc;
+		serial0 = &uart2;
+		serial1 = &uart3;
+		serial2 = &uart4;
+	};
+
 	chosen {
 		stdout-path = &uart2;
 	};
@@ -212,11 +220,13 @@ ethphy1: ethernet-phy@2 {
 	};
 };
 
+/* flexspi seems to break the FNG-System boot, disable it for now
 &flexspi {
 	pinctrl-names = "default";
 	pinctrl-0 = <&pinctrl_flexspi0>;
 	status = "okay";
 };
+*/
 
 &flexcan1 {
 	pinctrl-names = "default";