extract uimage output module into own file

modules/outputs/uimage.nix

@@ -0,0 +1,30 @@
+{
+  config,
+  pkgs,
+  lib,
+  ...
+}:
+let
+  inherit (lib) mkOption types concatStringsSep;
+  inherit (pkgs) liminix writeText;
+  o = config.system.outputs;
+in
+{
+  options.system.outputs.uimage = mkOption {
+    type = types.package;
+    internal = true;
+    description = ''
+      uimage
+      ******
+
+      Combined kernel and FDT in uImage (U-Boot compatible) format
+    '';
+  };
+  config.system.outputs.uimage = liminix.builders.uimage {
+    commandLine = concatStringsSep " " config.boot.commandLine;
+    inherit (config.boot) commandLineDtbNode;
+    inherit (config.hardware) loadAddress entryPoint alignment;
+    inherit (config.boot) imageFormat;
+    inherit (o) kernel dtb;
+  };
+}