[C72 Mini][DTS][RTC] Add alias for Real Time Clock

Use the alias rtc0 to force pcf2123 as the primary RTC for the system,
while relegating the internal snvs_rtc as secondary (rtc1)

arch/arm64/boot/dts/seco/seco-imx8mm-c72.dts

@@ -24,6 +24,11 @@
 	model = "SECO i.MX8MM C72 board";
 	compatible = "fsl,imx8mm-evk", "seco,imx8mm-c72","fsl,imx8mm";
 
+	aliases {
+		rtc1 = &snvs_rtc;
+		rtc0 = &rtc;
+	};
+
 	memory@40000000 {
 		device_type = "memory";
 		reg = <0x0 0x40000000 0 0x80000000>;