OMAPDSS: remove uses of __init/__exit

The following patches will add component handling to omapdss, improving
the handling of deferred probing. However, at the moment we're using
quite a lot of __inits and __exits in the driver, which prevent normal
dynamic probing and removal.

This patch removes most of the uses of __init and __exit, so that we can
register drivers after module init, and so that we can unregister
drivers even if the module is built-in.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>