board: sl28: add network variant 1 support

This variant has one network port connected via RGMII and doesn't have
any TSN capabilities out-of-the-box. Instead it has all four SerDes
lanes available for customer use.

Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>
diff --git a/arch/arm/dts/fsl-ls1028a-kontron-sl28-var1-u-boot.dtsi b/arch/arm/dts/fsl-ls1028a-kontron-sl28-var1-u-boot.dtsi
new file mode 100644
index 0000000..98e8939
--- /dev/null
+++ b/arch/arm/dts/fsl-ls1028a-kontron-sl28-var1-u-boot.dtsi
@@ -0,0 +1,8 @@
+// SPDX-License-Identifier: GPL-2.0+
+#include "fsl-ls1028a-kontron-sl28-u-boot.dtsi"
+
+/ {
+	aliases {
+		ethernet0 = &enetc1;
+	};
+};