LV2: allocation-free synchronization syscalls

* Show waiters' ID in kernel explorer.
* Remove deque dependency from sys_sync.h

rpcs3/Emu/Cell/SPUThread.h

@@ -815,6 +815,8 @@ public:
 	const u32 option; // sys_spu_thread_initialize option
 	const u32 lv2_id; // The actual id that is used by syscalls
 
+	atomic_t<spu_thread*> next_cpu{}; // LV2 thread queues' node link
+
 	// Thread name
 	atomic_ptr<std::string> spu_tname;