libata: simplify PCI legacy SFF host handling

With PCI resource fix up for legacy hosts.  We can use the same code
path to allocate IO resources and initialize host for both legacy and
native SFF hosts.  Only IRQ requesting needs to be different.

Rename ata_pci_*_native_host() to ata_pci_*_sff_host(), kill all
legacy specific functions and use the renamed functions instead.  This
simplifies code a lot.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Jeff Garzik <jeff@garzik.org>