libata-sff: separate out BMDMA init

Separate out ata_pci_bmdma_prepare_host() and ata_pci_bmdma_init_one()
from their SFF counterparts.  SFF ones no longer try to initialize
BMDMA or set PCI master.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>