ocl: Move static oclMat variables into FarnebackOpticalFlow class

Move some static functions into the FarnebackOpticalFlow class as well,
so they can access these new class variables.

oclMat objects cannot be declared statically, because their destructor
depends on the statically defined __module variable from cl_context.cpp.
Since statically defined variables in separate compilation units have
an undefined destruction order there is always the possibility the
__module will be destructed before an oclMat object, which results
in a segfault.

modules/ocl/include/opencv2/ocl/ocl.hpp

@@ -1473,6 +1473,16 @@ namespace cv
             void releaseMemory();
 
         private:
+            void setGaussianBlurKernel(const float *c_gKer, int ksizeHalf);
+
+            void gaussianBlurOcl(const oclMat &src, int ksizeHalf, oclMat &dst);
+
+            void polynomialExpansionOcl(
+                const oclMat &src, int polyN, oclMat &dst);
+
+            void gaussianBlur5Ocl(
+                const oclMat &src, int ksizeHalf, oclMat &dst);
+
             void prepareGaussian(
                 int n, double sigma, float *g, float *xg, float *xxg,
                 double &ig11, double &ig03, double &ig33, double &ig55);
@@ -1490,6 +1500,11 @@ namespace cv
             oclMat frames_[2];
             oclMat pyrLevel_[2], M_, bufM_, R_[2], blurredFrame_[2];
             std::vector<oclMat> pyramid0_, pyramid1_;
+            float ig[4];
+            oclMat gMat;
+            oclMat xgMat;
+            oclMat xxgMat;
+            oclMat gKerMat;
         };
 
         //////////////// build warping maps ////////////////////