[PATCH] libata: make per-dev transfer mode limits per-dev

Now that each ata_device has xfer masks, per-dev limits can be made
per-dev instead of per-port.  Make per-dev limits per-dev.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>