util/liveiso: Merge build scripts

Merge build scripts to `build.sh`. The new one takes the desired NixOS
config as an argument.

Example:
$ build.sh console.nix

Change-Id: I49360a5c57954a205c697a4ae07361779db2aa83
Signed-off-by: Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/60372
Reviewed-by: Michael Niewöhner <foss@mniewoehner.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

util/liveiso/build-console.sh

@@ -1,3 +0,0 @@
-#!/usr/bin/env sh
-
-nix-build '<nixpkgs/nixos>' -A config.system.build.isoImage -I nixos-config=console.nix

util/liveiso/build-graphical.sh

@@ -1,3 +0,0 @@
-#!/usr/bin/env sh
-
-nix-build '<nixpkgs/nixos>' -A config.system.build.isoImage -I nixos-config=graphical.nix

util/liveiso/build.sh

@@ -0,0 +1,13 @@
+#!/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