ide/ahci: Use universal DMA helper functions

ide/ahci: Use universal DMA helper functions

The AHCI device can provide both PCI and SysBus AHCI device
emulations.  For this reason, it wasn't previously converted to use
the pci_dma_*() helper functions.  Now that we have universal DMA
helper functions, this converts AHCI to use them.

The DMAContext is obtained from pci_dma_context() in the PCI case and
set to NULL in the SysBus case (i.e. we assume for now that a SysBus
AHCI has no IOMMU translation).

Cc: Kevin Wolf <[email protected]>
Cc: Michael S. Tsirkin <[email protected]>
Signed-off-by: David Gibson <[email protected]>
Signed-off-by: Benjamin Herrenschmidt <[email protected]>
Signed-off-by: Anthony Liguori <[email protected]>