Add fundamental list functions to manage log devices

This commit does the below things:
* Add fundamental list functions to manage log devices
* Fix a issue that if both log system and log apps are available, the
  latter will overwrite the devices->next!
* release memory at exit

Change-Id: Iebc3f8d2b34d6abbd834b07a31e0c2ebba01b63b
Signed-off-by: Chengwei Yang <chengwei.yang@intel.com>