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>
diff --git a/user_channel/channel_mgmt.hpp b/user_channel/channel_mgmt.hpp
index 09d2a71..8cdb9c7 100644
--- a/user_channel/channel_mgmt.hpp
+++ b/user_channel/channel_mgmt.hpp
@@ -38,12 +38,22 @@
 static constexpr const char* ipmiChMutexCleanupLockFile =
     "/var/lib/ipmi/ipmi_channel_mutex_cleanup";
 
+/** @struct ChannelAccessData
+ *
+ *  Structure to store both non-volatile and volatile channel access information
+ *  as used by IPMI specification (refer spec sec 22.22 to 22.24)
+ */
 struct ChannelAccessData
 {
     ChannelAccess chNonVolatileData;
     ChannelAccess chVolatileData;
 };
 
+/** @struct ChannelData
+ *
+ *  Structure for channel information - base structure to get all information
+ * about the channel.(refer spec sec 22.22 to 22.24)
+ */
 struct ChannelData
 {
     std::string chName;