move dts config from kernel to boot

The kernel does not need to know about the DTS. I am prepared
to be very slightly injured on this hill.

devices/gl-ar750/default.nix

@@ -42,6 +42,12 @@
       boot.tftp = {
         loadAddress = "0x00A00000";
       };
+      boot.dts = {
+        src = "${openwrt}/target/linux/ath79/dts/qca9531_glinet_gl-ar750.dts";
+        includes =  [
+          "${openwrt}/target/linux/ath79/dts"
+        ];
+      };
       kernel = {
         src = pkgs.pkgsBuildBuild.fetchurl {
           name = "linux.tar.gz";
@@ -61,12 +67,6 @@
           patches ${openwrt}/target/linux/generic/hack-5.15/*.patch
           patches ${openwrt}/target/linux/ath79/patches-5.15/*.patch
         '';
-        dts = {
-          src = "${openwrt}/target/linux/ath79/dts/qca9531_glinet_gl-ar750.dts";
-          includes =  [
-            "${openwrt}/target/linux/ath79/dts"
-          ];
-        };
         config = {
           MIPS_ELF_APPENDED_DTB = "y";
           OF = "y";