sis5513: factor out UDMA programming code

* Factor out UDMA programming code from sis_set_dma_mode() to per
  chipset family helpers: sis_{ata33,ata133}_program_udma_timings().

* Add sis_program_udma_timings() helper.

* Remove unneeded casts to 'unsigned long'.

* Minor cleanups.

There should be no functionality changes caused by this patch.

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