- Realize that the only place where ata_do_taskfile gets used is ide-disk.c
   move it and its "friends' over there.

 - Unify the do_request method for disk devices. This saves quite a lot of code.

 - Make task_muin_intr and task_in_intr use the same busy status checks on
   entry.

 - Unfold get_command at the single only place where it's used.

 - Add missing __ata_end_request on kill_rq path.

 - Rename udma_tcq_taskfile() to udma_tcq_init to make the code look like to
   normal udma_init. Revert the logics of udma_init and it's
   implementations to mirror that of udma_tcq_init().

 - Fix a tiny bug in pmac_udma_init() where it was reporting the wrong value up
   on failure.

 - Revert the logics of udma_start(). It's called from udma_init context.
   Realize that it is always returning ide_started. Make it self and the
   implementations of it return void.