ide: be able to build pmac driver without IDE built-in

No reason to need IDE built-in to be able to compile pmac driver.

Tested to work on 2.6.29-rc8 and 2.6.28.8 with ide and pmac as modules
inside an initramfs.

Signed-off-by: Gilles Espinasse <g.esp@free.fr>
Cc: sam@ravnborg.org
Cc: benh@kernel.crashing.org
[bart: remove now superfluous IDE check]
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>