services: port amdgpu services from private config

modules/services/hardware/amdgpu-common.nix

@@ -0,0 +1,17 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+{
+  options.services.amdgpu = {
+    cards = mkOption {
+      type = types.listOf types.str;
+      default = [ "card0" ];
+      example = literalExample ''[ "card0" ]'';
+      description = ''
+        A list of cards to enable fan configuration for. The identifiers for
+        each device can be found in /sys/class/drm/ as card0, card1, etc.
+      '';
+    };
+  };
+}