This series consolidates the code to implement configfs attributes
by providing the ->show and ->store method in common code and using
container_of in the methods to access the containing structure.

This reduces source and binary size of configfs consumers a lot.

Changes since V1:
 - a couple fixes for unintended changes in the uvc driver
 - moved a few CONFIG_ATTR() statements around
 - fixed up the documentation and samples in the last patch
 - added a little rather pointless blurb to the patch description for
   various patches