move all output modules to subdirectory, trash standard.nix

standard.nix isn't, is the essence here. Not all devices
support flashimage as it is currently defined - some
have diskimage, some have neither

modules/outputs/kexecboot.nix

@@ -0,0 +1,63 @@
+{
+  config
+, pkgs
+, lib
+, ...
+}:
+let
+  inherit (lib) mkOption mkForce types concatStringsSep;
+in {
+  imports = [ ../ramdisk.nix ];
+  options.system.outputs = {
+    kexecboot = mkOption {
+      type = types.package;
+      description = ''
+        Directory containing files needed for kexec booting.
+        Can be copied onto the target device using ssh or similar
+      '';
+    };
+    boot-sh = mkOption {
+      type = types.package;
+      description = ''
+        Shell script to run on the target device that invokes
+        kexec with appropriate options
+      '';
+    };
+  };
+  config = {
+    boot.ramdisk.enable = true;
+    system.outputs = {
+      kexecboot =
+        let o = config.system.outputs; in
+        pkgs.runCommand "kexecboot" {} ''
+          mkdir $out
+          cd $out
+          ln -s ${o.rootfs} rootfs
+          ln -s ${o.kernel} kernel
+          ln -s ${o.manifest} manifest
+          ln -s ${o.boot-sh} boot.sh
+          ln -s ${pkgs.kexec-tools-static}/bin/kexec ./kexec
+          ln -s ${o.dtb} dtb
+       '';
+
+      boot-sh =
+        let
+          inherit (pkgs.lib.trivial) toHexString;
+          inherit (config.system.outputs) rootfs kernel;
+          cmdline = concatStringsSep " " config.boot.commandLine;
+        in
+          pkgs.buildPackages.runCommand "boot.sh.sh" {
+          } ''
+            rootfsStart=${toString (100 * 1024 * 1024)}
+            rootfsBytes=$(stat -L -c %s ${rootfs})
+            append_cmd="mtdparts=phram0:''${rootfsBytes}(rootfs) phram.phram=phram0,''${rootfsStart},''${rootfsBytes} memmap=''${rootfsBytes}\$''${rootfsStart}";
+            cat > $out <<EOF
+            #!/bin/sh
+            test -d \$1
+            cd \$1
+            ./kexec -f -d --map-file rootfs@$rootfsStart --dtb dtb --command-line '${cmdline} $append_cmd' kernel
+            EOF
+          '';
+    };
+  };
+}