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/jffs2.nix

@@ -0,0 +1,46 @@
+{
+  config
+, pkgs
+, lib
+, ...
+}:
+let
+  inherit (lib) mkIf mkOption types;
+  o = config.system.outputs;
+in
+{
+  imports = [
+    ./initramfs.nix
+  ];
+
+  config = mkIf (config.rootfsType == "jffs2") {
+    kernel.config = {
+      JFFS2_FS = "y";
+      JFFS2_LZO = "y";
+      JFFS2_RTIME = "y";
+      JFFS2_COMPRESSION_OPTIONS = "y";
+      JFFS2_ZLIB = "y";
+      JFFS2_CMODE_SIZE = "y";
+    };
+    boot.initramfs.enable = true;
+    system.outputs = {
+      systemConfiguration =
+        pkgs.systemconfig config.filesystem.contents;
+      rootfs =
+        let
+          inherit (pkgs.pkgsBuildBuild) runCommand mtdutils;
+          endian = if pkgs.stdenv.isBigEndian
+                   then "--big-endian" else "--little-endian";
+        in runCommand "make-jffs2" {
+          depsBuildBuild = [ mtdutils ];
+        } ''
+          cp -a ${o.rootfsFiles} tmp
+          ${if config.boot.loader.extlinux.enable
+            then "(cd tmp && ln -s ${o.extlinux} boot)"
+            else ""
+          }
+          (cd tmp && mkfs.jffs2 --compression-mode=size ${endian} -e ${toString config.hardware.flash.eraseBlockSize} --enable-compressor=lzo --pad --root . --output $out --squash --faketime )
+        '';
+    };
+  };
+}