ThreadManager: Sync async reads on accurate gpu.

src/video_core/buffer_cache/buffer_cache.h

@@ -145,6 +145,18 @@ public:
         }
     }
 
+    bool MustFlushRegion(VAddr addr, std::size_t size) {
+        std::lock_guard lock{mutex};
+
+        std::vector<MapInterval> objects = GetMapsInRange(addr, size);
+        for (auto& object : objects) {
+            if (object->IsModified() && object->IsRegistered()) {
+                return true;
+            }
+        }
+        return false;
+    }
+
     /// Mark the specified region as being invalidated
     void InvalidateRegion(VAddr addr, u64 size) {
         std::lock_guard lock{mutex};