util/liveiso: Move NixOS configs to subdirectory

Move the NixOS configuration into a subdirectory so that configurations
for other distros can be added as well.

Change-Id: I0462c1a6541878c973be4302c5c5e9e9bfaed2a6
Signed-off-by: Felix Singer <felix.singer@secunet.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/73684
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-by: Michael Niewöhner <foss@mniewoehner.de>

util/liveiso/nixos/console.nix

@@ -0,0 +1,9 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+{
+	imports = [
+		./common.nix
+	];
+
+	services.getty.autologinUser = "user";
+}