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/pci/cs5535.c b/drivers/ide/pci/cs5535.c
index cd7c419..45f43ef 100644
--- a/drivers/ide/pci/cs5535.c
+++ b/drivers/ide/pci/cs5535.c
@@ -195,20 +195,19 @@
 
 static int cs5535_dma_check(ide_drive_t *drive)
 {
-	ide_hwif_t *hwif	= drive->hwif;
 	u8 speed;
 
 	drive->init_speed = 0;
 
 	if (ide_use_dma(drive) && cs5535_config_drive_for_dma(drive))
-		return hwif->ide_dma_on(drive);
+		return 0;
 
 	if (ide_use_fast_pio(drive)) {
 		speed = ide_get_best_pio_mode(drive, 255, 4, NULL);
 		cs5535_set_drive(drive, speed);
 	}
 
-	return hwif->ide_dma_off_quietly(drive);
+	return -1;
 }
 
 static u8 __devinit cs5535_cable_detect(struct pci_dev *dev)