alim15x3: backport short cables support from pata_ali.c

Backport short cables support from pata_ali.c and while at it cleanup
existing cable detection code.

This patch should allow UDMA > 2 modes on HP Pavilion N5430 and Fujitsu P2000.

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