pata_pdc2027x: Updates

Signed-off-by: Alan Cox <alan@redhat.com>

Correct missing modefilter (crash if BAR4 unassigned)
Use Cable Detect method
Wrap ->set_mode instead ready for ->post_set_mode removal
Maxtor errata as per Jeff Garzik report
Remove duplicated private udma_mask hacking
Signed-off-by: Jeff Garzik <jeff@garzik.org>