1. Let btvRegWeights to be constant per process call.

2. Let Farneback to be the default optical flow method.
3. Fix a timing method bug for ocl path.
4. Remove useless finish operation in farneback
5. Refactor buffer usage.

samples/gpu/super_resolution.cpp

@@ -221,7 +221,11 @@ int main(int argc, const char* argv[])
 
         if(useOcl)
         {
-            MEASURE_TIME(superRes->nextFrame(result_));
+            MEASURE_TIME(
+            {
+                superRes->nextFrame(result_);
+                ocl::finish();
+            });
         }
         else
 #endif