au1xxx-ide: use ide_tune_dma()

* Remove needless setting of drive->using_dma from auide_dma_check().

* Split off auide_mdma_filter() from auide_dma_check().

* Use ide_tune_dma() in auide_dma_check(), this fixes following issues:
  - device's DMA capability bit not being checked
  - device not being checked against generic DMA blacklist
  - transfer mode not being set on device/host

* Add PIO autotune fallback to auide_dma_check().

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