MySQL is heavily disk-bound. It is not CPU-bound except for things like sorting multi-gigabyte datasets, which people rarely use MySQL for. For most purposes you're better off installing more RAM than offloading computations to the GPU, otherwise MySQL has to spend all its time waiting for the harddisk.

I was surprised to discover that GPUs can accelerate SQLite http://pbbakkum.com/db/ and routing http://shader.kaist.edu/packetshader/ (although you're probably better off using an NP for routing).

Also, there are block modes that are seekable and thus could be parallelized if you had a big enough backlog, CTR mode in particular, but parallelizing individual streams is not likely to reap big enough rewards to justify the complexity.