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/Makefile b/arch/arm/dts/Makefile
index 858b79a..882ea02 100644
--- a/arch/arm/dts/Makefile
+++ b/arch/arm/dts/Makefile
@@ -438,6 +438,7 @@
 	fsl-ls1012a-frdm.dtb \
 	fsl-ls1012a-frwy.dtb
 dtb-$(CONFIG_TARGET_SL28) += fsl-ls1028a-kontron-sl28.dtb \
+	fsl-ls1028a-kontron-sl28-var1.dtb \
 	fsl-ls1028a-kontron-sl28-var3.dtb \
 	fsl-ls1028a-kontron-sl28-var4.dtb \