sgiseeq: convert to dma_alloc_noncoherent

Use the new non-coherent DMA API including proper ownership transfers.
This includes adding additional calls to dma_sync_desc_dev as the
old syncing was rather ad-hoc.

Thanks to Thomas Bogendoerfer for debugging the ownership transfer
issues.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>