COMPMID-1707: Create 3 special CLWidthConcatenate kernel to concatenate 2/4 and 8 tensors (Part 1)

Creating special cases for concatening 2 and 4 tensors.

Change-Id: I6a739a494ae45011acb65369e353f9ef96970b90
diff --git a/tests/validation/fixtures/WidthConcatenateLayerFixture.h b/tests/validation/fixtures/WidthConcatenateLayerFixture.h
index caad0fe..1f79210 100644
--- a/tests/validation/fixtures/WidthConcatenateLayerFixture.h
+++ b/tests/validation/fixtures/WidthConcatenateLayerFixture.h
@@ -52,7 +52,7 @@
     {
         // Create input shapes
         std::mt19937                    gen(library->seed());
-        std::uniform_int_distribution<> num_dis(2, 4);
+        std::uniform_int_distribution<> num_dis(2, 8);
         const int                       num_tensors = num_dis(gen);
 
         std::vector<TensorShape>         shapes(num_tensors, shape);