pata_via: store UDMA masks in via_isa_bridges table

* store UDMA masks in via_isa_bridges[] and while at it make "flags"
  field to be u8 instead of u16

* convert the driver to use UDMA masks from via_isa_bridges[]

* remove no longer needed VIA_UDMA* defines

Make some minor documentation and CodingStyle fixes while at it.
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>