dma_addr_t sn_dma_map_single (struct device * dev, void * cpu_addr, size_t size, int direction);
Map the region pointed to by cpu_addr for DMA and return the DMA address.
We map this to the one step pcibr_dmamap_trans interface rather than the two step pcibr_dmamap_alloc/pcibr_dmamap_addr because we have no way of saving the dmamap handle from the alloc to later free (which is pretty much unacceptable).
simplify our interface; figure out how to save dmamap handle so can use two step.