ide: add ide_tune_dma() helper

After reworking the code responsible for selecting the best DMA
transfer mode it is now possible to add generic ide_tune_dma() helper.

Convert some IDE PCI host drivers to use it (the ones left need more work).

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

diff --git a/drivers/ide/pci/slc90e66.c b/drivers/ide/pci/slc90e66.c
index 9e95a5c..c40f291 100644
--- a/drivers/ide/pci/slc90e66.c
+++ b/drivers/ide/pci/slc90e66.c
@@ -160,22 +160,11 @@
 	return ide_config_drive_speed(drive, speed);
 }
 
-static int slc90e66_config_drive_for_dma (ide_drive_t *drive)
-{
-	u8 speed = ide_max_dma_mode(drive);
-
-	if (!speed)
-		return 0;
-
-	(void) slc90e66_tune_chipset(drive, speed);
-	return ide_dma_enable(drive);
-}
-
 static int slc90e66_config_drive_xfer_rate (ide_drive_t *drive)
 {
 	drive->init_speed = 0;
 
-	if (ide_use_dma(drive) && slc90e66_config_drive_for_dma(drive))
+	if (ide_tune_dma(drive))
 		return 0;
 
 	if (ide_use_fast_pio(drive))