doxygen: Remove bitrotted Doxygen grouping directives

I had grand plans for Waffle's Doxygen. @defgroup, @ingroup,
@addtogroup, OH MY! The intent was that documentation for modules and
classes would be logically grouped in the Doxygen output. Alas, these
plans never really happened and Waffle's Doxygen grouping is a mess.

Mercy kill the Doxygen grouping directives. They can always be
resurrected if someone cares to clean it up.

Signed-off-by: Chad Versace <chad.versace@linux.intel.com>
doxygen: Clean up @file directives

- Remove filename from @file directives. The filename should remain
  autodetected, otherwise the doxygen block becomes orphaned when the file
  becomes renamed.
- Don't put brief comments in @file. They go in @brief.

Signed-off-by: Chad Versace <chad.versace@linux.intel.com>