VideoSW: Use more VideoCommon

Now we require lots of empty functions, but this removes by far more duplicated code.

Source/Core/VideoCommon/CPMemory.h

@@ -257,6 +257,7 @@ struct CPState final
 	BitSet32 attr_dirty;
 	bool bases_dirty;
 	VertexLoaderBase* vertex_loaders[8];
+	int last_id;
 };
 
 class PointerWrap;