PCI IDE DMA standard (or "bmdma") helper routines ata_bmdma_stop,
ata_bmdma_ack_irq, and ata_bmdma_status are added to linux/libata.h,
and used in libata-core.

There is a minor behavior change, such that, the Alt Status register
is read before acknowledging the bmdma interrupt.  This should be ok,
and furthermore there will be more significant behavior changes
in this area coming soon.