atiixp.c: add cable detection support for ATI IDE

IDE HDD does not work if it uses a 40-pin PATA cable on ATI chipset.
This patch fixes the bug.

Signed-off-by: Conke Hu <conke.hu@amd.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>