[GPU] Unified clear_memory_page_state to be used in D3D12 & Vulkan

src/xenia/gpu/command_processor.h

@@ -33,6 +33,12 @@ class ByteStream;
 
 namespace gpu {
 
+enum class CommonGPUSetting {
+  ClearMemoryPageState,
+};
+
+void CommonSaveGPUSetting(CommonGPUSetting setting, uint64_t value);
+
 class GraphicsSystem;
 class Shader;