[ide] add ide_hwif_t->dma_setup()

[ide] add ide_hwif_t->dma_setup()

* tag REQ_DRIVE_TASKFILE write requests with REQ_RW
* split off ->dma_setup() from ->ide_dma_[read,write] functions
* use ->dma_setup() directly in ATAPI drivers and remove media
  checks from ->ide_dma_[read,write]
* ->ide_dma_[read,write,begin] cannot fail now
* in Etrax ide.c setup DMA for ATAPI devices before sending
  command to drive (so setup order is the same as for disks)

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