Set hwif->ide_dma_{check,on} and hwif->autodma to 1 after checking that
->dma_base exists.  If ->dma_base is not set (== PCI BAR4 cannot be reserved)
then DMA hooks shouldn't be initialized or bad things will happen.
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>