ide: switch to DMA-mapping API

* pci_map_sg() -> dma_map_sg() in ide_build_sglist().

* pci_unmap_sg() -> dma_unmap_sg() in ide_destroy_dmatable().

There should be no functionality changes caused by this patch except
for blackfin arch whose dma_[un]map_sg() implementation differs from
pci_[un]map_sg() one (on s390 arch there is no PCI, on avr32 and h8300
archs PCI is currently unsupported, on m32r arch PCI support depends
on BROKEN, on m68k arch PCI support depends on HADES which in turn
depends on BROKEN, on all other archs dma_[un]map_sg() functionality
matches with pci_[un]map_sg() one).

blackfin behavior change was ack-ed by Bryan Wu.

Cc: Bryan Wu <bryan.wu@analog.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>