[DTBO][D18][MV] Remap serial ports to match mapping on older platforms

Modular Vision was designed to have the same form factor as Santaro
(SBC-SANTARO-MX6), so generally internal device mapping should also be
the same when possible.

This adds aliases entries to the MV overlay to remap the serial ports.

MODV-114

arch/arm64/boot/dts/seco/overlays/seco-imx8mp-d18-mv-overlay.dts

@@ -19,6 +19,17 @@
 			model = "SECO Modular Vision with i.MX8MPlus LPDDR4 D18";
 			compatible = "fsl,imx8mp-evk", "seco,imx8mp-d18", "fsl,imx8mp";
 
+			aliases {
+				/* RS232 #1 ( Debug serial port) on ttymx0 */
+				serial0 = "/soc@0/bus@30800000/serial@30890000";
+				/* RS232 #2 ( MDB ) on ttymx1 */
+				serial1 = "/soc@0/bus@30800000/serial@30860000";
+				/* RS485 on ttymx2 */
+				serial2 = "/soc@0/bus@30800000/serial@30a60000";
+				/* For completeness, also remap serial3 */
+				serial3 = "/soc@0/bus@30800000/serial@30880000";
+			};
+
 			seco-device-config {
 				/*
 				 * This node is parsed in U-Boot to resolve the