FifoManager: Extract RestoreState from PauseAndLock

Replace calls of FifoManager::PauseAndLock(do_lock=false) with new
function RestoreState for clarity.

Source/Core/DolphinQt/Host.cpp

@@ -108,7 +108,7 @@ static void RunWithGPUThreadInactive(std::function<void()> f)
     auto& fifo = system.GetFifo();
     fifo.PauseAndLock(true, was_running);
     f();
-    fifo.PauseAndLock(false, was_running);
+    fifo.RestoreState(was_running);
   }
   else
   {