yuzu: create linux group in general settings

- Create files dedicated to starting and stopping gamemode functions
  - Use them in yuzu and yuzu_cmd modules

src/common/linux/gamemode.cpp

@@ -0,0 +1,39 @@
+// SPDX-FileCopyrightText: Copyright 2023 yuzu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <gamemode_client.h>
+
+#include "common/linux/gamemode.h"
+#include "common/settings.h"
+
+namespace Common::Linux {
+
+void StartGamemode() {
+    if (Settings::values.enable_gamemode) {
+        if (gamemode_request_start() < 0) {
+            LOG_WARNING(Frontend, "Failed to start gamemode: {}", gamemode_error_string());
+        } else {
+            LOG_INFO(Frontend, "Started gamemode");
+        }
+    }
+}
+
+void StopGamemode() {
+    if (Settings::values.enable_gamemode) {
+        if (gamemode_request_end() < 0) {
+            LOG_WARNING(Frontend, "Failed to stop gamemode: {}", gamemode_error_string());
+        } else {
+            LOG_INFO(Frontend, "Stopped gamemode");
+        }
+    }
+}
+
+void SetGamemodeState(bool state) {
+    if (state) {
+        StartGamemode();
+    } else {
+        StopGamemode();
+    }
+}
+
+} // namespace Common::Linux