workqueue: Make schedule_work() available again to non GPL modules

Commit 8425e3d5

 ("workqueue: inline trivial wrappers") changed
schedule_work() and schedule_delayed_work() to inline wrappers,
but these rely on some symbols that are EXPORT_SYMBOL_GPL, while
the original functions were EXPORT_SYMBOL.  This has the effect of
changing the licensing requirement for these functions and making
them unavailable to non GPL modules.

Make them available again by removing the restriction on the
required symbols.

Signed-off-by: Marc Dionne <marc.dionne@your-file-system.com>
Signed-off-by: Tejun Heo <tj@kernel.org>