Add Texture Deposterization

Even with hybrid scaling, some textures were still slightly posterized. This is because a lot of them come from low color depth (e.g. 4444/565 or compressed) formats. Since we are using 8888 anyway when scaling why not make use of it? 

The effect is rather minor (to invisible) in most cases, but it helps greatly in some, and the performance impact is negligible compared to scaling.