alim15x3: use ide_tune_dma()

Use ide_tune_dma() in ali15x3_config_drive_for_dma() and remove all the open
coded DMA tuning code and also config_chipset_for_dma().  Set ->atapi_dma flag
correctly in init_hwif_common_ali15x3() so ide_tune_dma() can take care of
checking if ATAPI DMA is allowed and remove open coded ATAPI DMA check from
ali15x3_config_drive_for_dma().

There should be no functionality changes caused by this patch.

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