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/build.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env sh
+
+config=$1
+
+if [ -z "$config" ] || [ ! -f "$config" ]; then
+	echo "Usage: $0 <config.nix>"
+	echo "No config given. Exiting."
+	exit 1
+fi
+
+nix-build '<nixpkgs/nixos>' \
+	-A config.system.build.isoImage \
+	-I nixos-config=$config \
+	-I nixpkgs=https://github.com/NixOS/nixpkgs/archive/refs/heads/nixos-22.11.tar.gz