au1xxx-ide: fix MWDMA support

Always use "fast" MWDMA support and remove dma_{black,white}_list
(they were based on completely bogus ->ide_dma_check implementation
which didn't set neither the host controller timings nor the device
for the desired transfer mode).

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