doxygen: score: adjust doc in stackimpl.h to doxygen guidelines

Update #3706.

cpukit/include/rtems/score/states.h

@@ -1,6 +1,8 @@
 /**
  * @file
  *
+ * @ingroup RTEMSScoreStates
+ *
  * @brief Thread Execution State Information
  *
  * This include file defines thread execution state information.
@@ -29,10 +31,13 @@ extern "C" {
  *
  * @ingroup RTEMSScore
  *
+ * @brief SuperCore Thread States
+ *
  * This handler encapsulates functionality which relates to the management of
  * the state bitmap associated with each thread.
+ *
+ * @{
  */
-/**@{*/
 
 /**
  *  The following type defines the control block used to manage a
@@ -40,7 +45,7 @@ extern "C" {
  */
 typedef uint32_t   States_Control;
 
-/**@}*/
+/** @} */
 
 #ifdef __cplusplus
 }