ide: merge ->dma_host_{on,off} methods into ->dma_host_set method

Merge ->dma_host_{on,off} methods into ->dma_host_set method
which takes 'int on' argument.

There should be no functionality changes caused by this patch.

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