staging: comedi: Add helper macro for comedi_driver boilerplate

Introduce the module_comedi_driver macro which is a convenience
macro for comedi driver modules similar to module_platform_driver.
It is intended to be used by drivers where the init/exit section
does nothing but register/unregister the comedi driver. By using
this macro it is possible to eliminate a few lines of boilerplate
code per comedi driver.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: Mori Hess <fmhess@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>