ide: Documentation/ide/ide.txt fixes

* "hdx=cyls,heads,sects,wpcom,irq" should be "hdx=cyls,heads,sects".

* "hdx=" is for "x" from 'a' to 'u', "idex=" is for "x" from '0' to '9'.

* "idex=noautotune" is long gone.

* Obsoleted "ide0=" parameters were already removed from the documentation.

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>