hpt366: MWDMA filter for SATA cards (take 2)

The Marvell bridge chips used on HighPoint SATA cards do not seem to support
the MWDMA modes (at least that could be seen in their so-called drivers :-),
so the driver needs to account for this -- to achieve this:

- add mdma_filter() method from the original patch by Bartlomiej Zolnierkiewicz
  with his consent;

- install the method for all chips to only return empty mask if a SATA drive
  is detected on HPT372{AN]/374 chips...

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