SWDEV-272496 - Detect callbacks and force AQL barrier

HIP tests require HIP callbacks to be processed in another thread.
This change will use a thread from HSA signal callbacks to make
sure a HIP callback was done asynchronously.
Also process the callback before changing the status of command

Change-Id: Icef85d0e0f808663882cf6881ff1be3e5eca29ac

rocclr/platform/command.hpp

@@ -204,6 +204,9 @@ class Event : public RuntimeObject {
 
   //! RTTI internal implementation
   virtual ObjectType objectType() const { return ObjectTypeEvent; }
+
+  //! Returns the callback for this event
+  const CallBackEntry* Callback() const { return callbacks_; }
 };
 
 /*! \brief An operation that is submitted to a command queue.