Doxygen comments for enum & structure

Added doxygen comments for enums & structures for user & channel
layers.

Unit-test:
verified build.

Change-Id: Ie5af8d6cdd4c04cb396869b7a3dc44f84efedd19
Signed-off-by: Richard Marian Thomaiyar <richard.marian.thomaiyar@linux.intel.com>
8 files changed