arm64: dts: imx8mp: Add missing LED enumerators for DH electronics i.MX8M Plus DHCOM on PDK2

The LED enumerators are missing, which prevents the LEDs from being
accurately told apart by label. Fill in the enumerators the same way
they are already present on PDK3. Put this into local DT extras until
matching kernel patch lands in Linux.

Signed-off-by: Marek Vasut <marek.vasut@mailbox.org>
Reviewed-by: Peng Fan <peng.fan@nxp.com>

arch/arm/dts/imx8mp-dhcom-pdk2-u-boot.dtsi

@@ -4,3 +4,23 @@
  */
 
 #include "imx8mp-dhcom-u-boot.dtsi"
+
+/ {
+	led {
+		led-0 {
+			function-enumerator = <0>;
+		};
+
+		led-1 {
+			function-enumerator = <1>;
+		};
+
+		led-2 {
+			function-enumerator = <2>;
+		};
+
+		led-3 {
+			function-enumerator = <3>;
+		};
+	};
+};