it8213/piix/slc90e66: "de-couple" PIO and UDMA modes

Don't force PIO4 when programming UDMA mode (suggested by Sergei).

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