Allow user to change DPLII decoding quality

Source/Core/AudioCommon/Enums.h

@@ -0,0 +1,16 @@
+// Copyright 2019 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#pragma once
+
+namespace AudioCommon
+{
+enum class DPL2Quality
+{
+  Low = 0,
+  Medium = 1,
+  High = 2,
+  Highest = 3
+};
+}  // namespace AudioCommon