Factor out setting PCI bus-mastering from ide_hwif_setup_dma()
to ide_pci_set_master() helper.

While at it:

* don't read PCI Command register if not necessary

* use PCI device name instead of hwif->name

* cleanup ide_hwif_setup_dma() a bit
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>