modules/image: move extlinux population into extraBootFiles hook

modules/image.nix

@@ -121,10 +121,9 @@ in
 
       (
         cd files
-        echo "running installBootLoader"
-        ${config.boot.loader.generic-extlinux-compatible.populateCmd} -c ${config.system.build.toplevel} -d .
-        echo "ran installBootLoader"
+        echo "installing extraBootFiles"
         for d in ${lib.escapeShellArgs cfg.extraBootFiles}; do
+          echo "installing '$d'"
           cp -R $d/* ./
         done
         echo "copied extraBootFiles"
@@ -382,5 +381,11 @@ in
         chmod -w $out
       ''
     );
+
+    sane.image.extraBootFiles = lib.optionals config.boot.loader.generic-extlinux-compatible.enable [
+      (pkgs.runCommandLocal "populate-extlinux" {} ''
+        ${config.boot.loader.generic-extlinux-compatible.populateCmd} -c ${config.system.build.toplevel} -d "$out"
+      '')
+    ];
   };
 }