pdc202xx_old: remove broken SWDMA support

Documentation doesn't mention SWDMA and moreover all timings used
for SWDMA modes were over-clocked when compared to ATA spec.

Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>