scsi: am53c974: use the generic DMA API

Remove usage of the legacy PCI DMA API.  To make this easier we also
store a struct device instead of pci_dev in the dev field of struct
esp.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>