textures/decoders: Fix block linear to pitch copies

There were two issues with block linear copies. First the swizzling was
wrong and this commit reimplements them.

The other issue was that these copies are generally used to download
render targets from the GPU and yuzu was not downloading them from
host GPU memory unless the extreme GPU accuracy setting was selected.
This commit enables cached memory reads for all accuracy levels.

- Fixes level thumbnails in Super Mario Maker 2.