ide: add ide_set_dma() helper (v2)

* add ide_set_dma() helper and make ide_hwif_t.ide_dma_check return
  -1 when DMA needs to be disabled (== need to call ->ide_dma_off_quietly)
   0 when DMA needs to be enabled  (== need to call ->ide_dma_on)
   1 when DMA setting shouldn't be changed
* fix IDE code to use ide_set_dma() instead if using ->ide_dma_check directly

v2:
* updated for scc_pata

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>

diff --git a/drivers/ide/ide-io.c b/drivers/ide/ide-io.c
index 99d1c43..9f45a84 100644
--- a/drivers/ide/ide-io.c
+++ b/drivers/ide/ide-io.c
@@ -226,7 +226,7 @@
 			break;
 		if (drive->hwif->ide_dma_check == NULL)
 			break;
-		drive->hwif->ide_dma_check(drive);
+		ide_set_dma(drive);
 		break;
 	}
 	pm->pm_step = ide_pm_state_completed;