fujitsu-laptop: support led-class as module

Support fujitsu-laptop with led-class built as a module instead of
being compiled in.

Signed-off-by: Stephen Gildea <stepheng+linux@gildea.com>
Acked-by: Jonathan Woithe <jwoithe@physics.adelaide.edu.au>
Signed-off-by: Len Brown <len.brown@intel.com>