cmd64x: remove /proc/ide/cmd64x

This belongs to user-space (and only if really needed).

   text    data     bss     dec     hex filename
   3874     180      28    4082     ff2 drivers/ide/pci/cmd64x.o.before
   2231     180       0    2411     96b drivers/ide/pci/cmd64x.o.after

Additionaly to being bloat the code reported incorrect UDMA modes for
the reserved values of UDIDETCR0/1 registers.

Also while at it remove unused CNTRL_DIS_RA0/1 defines.

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