alim15x3: skip DMA initialization completely on revs < 0x20

Skip DMA initialization completely on revs < 0x20 by setting IDE_HFLAG_NO_DMA
host flag and resetting DMA host masks in alim15x3_init_one() (currently
ide_hwif_setup_dma() will try to obtain DMA base and setup PCI bus-mastering
but init_dma_ali15x3() will fail).

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