Use condition var to properly pause the CPU thread

Adds support for threaded pausing so citra doesn't spin wait on pause

src/citra_qt/bootmanager.cpp

@@ -59,6 +59,9 @@ void EmuThread::run() {
             yieldCurrentThread();
             
             was_active = false;
+        } else {
+            std::unique_lock<std::mutex> lock(running_mutex);
+            running_cv.wait(lock, [this]{ return IsRunning() || stop_run; });
         }
     }