- Eliminate ide_task_t and rename struct ide_task_s to struct ata_taskfile.
   This should become the entity which is holding all data for a request in the
   future. If this turns out to be the case, we will just rename it to
   ata_request.

- Reduce the number of arguments for the ata_taskfile() function. This helps to
   wipe quite a lot of code out as well.

This stage is not sensitive, so let's make a patch before we start to integrate
the last work of Jens Axboe.