libata: reduce ata_pci_[sff,bmdma]_init_one() size

Turn both helpers (which are used only during LLDs initialization
time and thus are not performance sensitive) into wrappers around
the new ata_pci_init_one() function, this cuts 20 LOC and saves
~1.1k of the output code size (x86-64):

 text    data     bss     dec     hex filename
  21392       0      19   21411    53a3 drivers/ata/libata-sff.o.before
  20256       0      19   20275    4f33 drivers/ata/libata-sff.o.after

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>