[Task] Fix asynchronous cancel for Task

Signed-off-by: Regis Merlino <regis.merlino@intel.com>
[Task Processor] Add a finally callback

Signed-off-by: Regis Merlino <regis.merlino@intel.com>
[Task Processor] API cleanup

Signed-off-by: Regis Merlino <regis.merlino@intel.com>
[Tasks] Structure re-arch for rsu_task_t and rsu_async_cb_data_t

Signed-off-by: Regis Merlino <regis.merlino@intel.com>
[Tasks] Simplify many function prototypes following the struct re-arch for tasks

Signed-off-by: Regis Merlino <regis.merlino@intel.com>