pata_octeon_cf: perform host detach, removal on exit

This driver does not detach and remove its ata_host properly on device
removal. Add the common .remove helper.

Note: I do not know this driver well enough to ensure this is the right
thing to do. Merge this patch with caution.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: David Daney <david.daney@cavium.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>