[libata] struct pci_dev related cleanups

* remove pointless pci_dev_to_dev() wrapper.  Just directly reference
  the embedded struct device like everyone else does.

* pata_cs5520: delete cs5520_remove_one(), it was a duplicate of
  ata_pci_remove_one()

* linux/libata.h: don't bother including linux/pci.h, we don't need it.
  Simply declare 'struct pci_dev' and assume interested parties will
  include the header, as they should be doing anyway.

* linux/libata.h: consolidate all CONFIG_PCI declarations into a
  single location in the header.

Signed-off-by: Jeff Garzik <jgarzik@redhat.com>