ide-pmac: use ->init_dma method

* Move pmif->dma_regs check from pmac_ide_setup_device() to
  pmac_ide_init_dma().

* Get 'pmif' from 'hwif->hwif_data' in pmac_ide_init_dma() and replace
  'pmac_ide_hwif_t *pmif' argument by 'const struct ide_port_info *d'.

* Add pmac_ide_init_dma() implementation for CONFIG_BLK_DEV_IDEDMA_PMAC=n
  case and convert the driver to use ->init_dma method.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>