Staging: comedi: enable it to build on all arches

Hopefully all of the arch-specific problems are now resolved, so let's
let this subsystem be enabled on all arches.  If there are problems
found, we will fix them up.

Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: H Hartley Sweeten <hartleys@visionengravers.com>
Cc: Bernd Porr <mail@berndporr.me.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>