ide: remove obsoleted "idex=base[,ctl[,irq]]" kernel parameters (take 2)

* Remove obsoleted "idex=base[,ctl[,irq]]" kernel parameters
  and update Documentation/ide/ide.txt.

* Remove no longer needed ide_forced chipset type.

v2:
* is_chipset_set[] -> is_chipset_set in ide.c.

* Documentation/ide/ide.txt fix.

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