scc_pata: add ->dma_host_set and ->dma_start methods

Add ->dma_host_set and ->dma_start methods (+ __scc_dma_end() helper)
so scc_ide_{in,out}b() can be used directly.

There should be no functional changes caused by this patch.

Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>