feat(image): install upstream kexec which now have support for UKIs

pkgs/image/default.nix

@@ -0,0 +1,36 @@
+{
+  pkgs,
+  stdenvNoCC,
+  patosPkgs,
+  version,
+  ...
+}:
+let
+  pname = "patos-image";
+in
+stdenvNoCC.mkDerivation (finalAttrs: {
+  inherit version;
+  inherit pname;
+
+  buildInputs = with pkgs; [
+    erofs-utils
+    dosfstools
+    mtools
+    e2fsprogs
+  ];
+
+  env = {
+    # vfat options won't efi won't find the fs otherwise.
+    SYSTEMD_REPART_MKFS_OPTIONS_VFAT = "-S 512 -c";
+  };
+
+  systemd = patosPkgs.systemd.out;
+  kernel = patosPkgs.kernel.kernel;
+  initrd = patosPkgs.initrd.out;
+  rootfs = patosPkgs.rootfs.out;
+
+  #FIXME: use roothash instead of device.
+  kernelCmdLine = "root=/dev/sda2 console=ttyS0";
+
+  builder = ./mkimage.sh;
+})