libata: convert native PCI host handling to new init model

Convert native PCI host handling to alloc-init-register model.  New
function ata_pci_init_native_host() follows the new init model and
replaces ata_pci_init_native_mode().  As there are remaining LLD
users, the old function isn't removed yet.

ata_pci_init_one() is reimplemented using the new function and now
fully converted to new init model.

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