zfreeze: cache vertex positions

Suggested by degasus.

Source/Core/VideoCommon/VertexLoaderManager.cpp

@@ -26,6 +26,9 @@
 namespace VertexLoaderManager
 {
 
+float position_cache[3][4];
+u32 position_matrix_index[3];
+
 typedef std::unordered_map<PortableVertexDeclaration, std::unique_ptr<NativeVertexFormat>> NativeVertexFormatMap;
 static NativeVertexFormatMap s_native_vertex_map;
 static NativeVertexFormat* s_current_vtx_fmt;