staging: comedi: tests: add unittest framework for comedi

Adds a framework for unittests for comedi drivers.  It was certainly
possible to write some unit tests before and test various aspects of a
particular driver, but this framework makes this a bit easier and hopefully
inspires more unittest modules to be written.

Signed-off-by: Spencer E. Olson <olsonse@umich.edu>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>