ide: remove "idex=dma" kernel parameter

It has been obsoleted since 1 Nov 2004, is valid only when used together with
"ide=nodma" kernel parameter (which makes no sense) and only for aec62xx,
cmd64x, cs5220, generic, hpt366, sl82c105, tc86c001 and triflex host drivers.

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