Redefine the removed __dev* for now

The __dev* directives and functions were removed in 3.8, as they
are no-ops. We still have use of them for older versions, thus
we should define them (as noops) if they don't exist.

Signed-off-by: Tzafrir Cohen <tzafrir.cohen@xorcom.com>
Acked-by: Shaun Ruffell <sruffell@digium.com>