arm64: dts: freescale: Use overlay target for simplicity

With commit 15d16d6d ("kbuild: Add generic rule to apply
fdtoverlay"), overlay target can be used to simplify the build of DTB
overlays.  It also performs a cross check to ensure base DT and overlay
actually match.
Signed-off-by: Shawn Guo <shawnguo@kernel.org>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>

arch/arm64/boot/dts/freescale/Makefile

 # SPDX-License-Identifier: GPL-2.0
 
-# required for overlay support
-DTC_FLAGS_fsl-ls1028a-qds := -@
-DTC_FLAGS_fsl-ls1028a-qds-13bb := -@
-DTC_FLAGS_fsl-ls1028a-qds-65bb := -@
-DTC_FLAGS_fsl-ls1028a-qds-7777 := -@
-DTC_FLAGS_fsl-ls1028a-qds-85bb := -@
-DTC_FLAGS_fsl-ls1028a-qds-899b := -@
-DTC_FLAGS_fsl-ls1028a-qds-9999 := -@
-
 dtb-$(CONFIG_ARCH_LAYERSCAPE) += fsl-ls1012a-frdm.dtb
 dtb-$(CONFIG_ARCH_LAYERSCAPE) += fsl-ls1012a-frwy.dtb
 dtb-$(CONFIG_ARCH_LAYERSCAPE) += fsl-ls1012a-oxalis.dtb
@@ -21,12 +12,6 @@ dtb-$(CONFIG_ARCH_LAYERSCAPE) += fsl-ls1028a-kontron-sl28-var2.dtb
 dtb-$(CONFIG_ARCH_LAYERSCAPE) += fsl-ls1028a-kontron-sl28-var3-ads2.dtb
 dtb-$(CONFIG_ARCH_LAYERSCAPE) += fsl-ls1028a-kontron-sl28-var4.dtb
 dtb-$(CONFIG_ARCH_LAYERSCAPE) += fsl-ls1028a-qds.dtb
-dtb-$(CONFIG_ARCH_LAYERSCAPE) += fsl-ls1028a-qds-13bb.dtb
-dtb-$(CONFIG_ARCH_LAYERSCAPE) += fsl-ls1028a-qds-65bb.dtb
-dtb-$(CONFIG_ARCH_LAYERSCAPE) += fsl-ls1028a-qds-7777.dtb
-dtb-$(CONFIG_ARCH_LAYERSCAPE) += fsl-ls1028a-qds-85bb.dtb
-dtb-$(CONFIG_ARCH_LAYERSCAPE) += fsl-ls1028a-qds-899b.dtb
-dtb-$(CONFIG_ARCH_LAYERSCAPE) += fsl-ls1028a-qds-9999.dtb
 dtb-$(CONFIG_ARCH_LAYERSCAPE) += fsl-ls1028a-rdb.dtb
 dtb-$(CONFIG_ARCH_LAYERSCAPE) += fsl-ls1043a-qds.dtb
 dtb-$(CONFIG_ARCH_LAYERSCAPE) += fsl-ls1043a-rdb.dtb
@@ -49,6 +34,20 @@ dtb-$(CONFIG_ARCH_LAYERSCAPE) += fsl-lx2160a-qds.dtb
 dtb-$(CONFIG_ARCH_LAYERSCAPE) += fsl-lx2160a-rdb.dtb
 dtb-$(CONFIG_ARCH_LAYERSCAPE) += fsl-lx2162a-qds.dtb
 
+fsl-ls1028a-qds-13bb-dtbs := fsl-ls1028a-qds.dtb fsl-ls1028a-qds-13bb.dtbo
+fsl-ls1028a-qds-65bb-dtbs := fsl-ls1028a-qds.dtb fsl-ls1028a-qds-65bb.dtbo
+fsl-ls1028a-qds-7777-dtbs := fsl-ls1028a-qds.dtb fsl-ls1028a-qds-7777.dtbo
+fsl-ls1028a-qds-85bb-dtbs := fsl-ls1028a-qds.dtb fsl-ls1028a-qds-85bb.dtbo
+fsl-ls1028a-qds-899b-dtbs := fsl-ls1028a-qds.dtb fsl-ls1028a-qds-899b.dtbo
+fsl-ls1028a-qds-9999-dtbs := fsl-ls1028a-qds.dtb fsl-ls1028a-qds-9999.dtbo
+
+dtb-$(CONFIG_ARCH_LAYERSCAPE) += fsl-ls1028a-qds-13bb.dtb
+dtb-$(CONFIG_ARCH_LAYERSCAPE) += fsl-ls1028a-qds-65bb.dtb
+dtb-$(CONFIG_ARCH_LAYERSCAPE) += fsl-ls1028a-qds-7777.dtb
+dtb-$(CONFIG_ARCH_LAYERSCAPE) += fsl-ls1028a-qds-85bb.dtb
+dtb-$(CONFIG_ARCH_LAYERSCAPE) += fsl-ls1028a-qds-899b.dtb
+dtb-$(CONFIG_ARCH_LAYERSCAPE) += fsl-ls1028a-qds-9999.dtb
+
 dtb-$(CONFIG_ARCH_MXC) += imx8mm-beacon-kit.dtb
 dtb-$(CONFIG_ARCH_MXC) += imx8mm-ddr4-evk.dtb
 dtb-$(CONFIG_ARCH_MXC) += imx8mm-emcon-avari.dtb