Improve start-up time for concatenation layers

 - pass tensor's dimensions at runtime rather than compile time
 - Add guard macro to compile only kernel of internest

Resolves: COMPMID-5121
Signed-off-by: Ramy Elgammal <ramy.elgammal@arm.com>
Change-Id: I76b7c0cf56d803f58ebff5494c904ace2a86ef5a
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/7097
Tested-by: Arm Jenkins <bsgcomp@arm.com>
Reviewed-by: Gian Marco Iodice <gianmarco.iodice@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
diff --git a/src/gpu/cl/kernels/ClWidthConcatenateKernel.h b/src/gpu/cl/kernels/ClWidthConcatenateKernel.h
index 71df077..3ace440 100644
--- a/src/gpu/cl/kernels/ClWidthConcatenateKernel.h
+++ b/src/gpu/cl/kernels/ClWidthConcatenateKernel.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021 Arm Limited.
+ * Copyright (c) 2021-2022 Arm Limited.
  *
  * SPDX-License-Identifier: MIT
  *
@@ -61,6 +61,9 @@
 
     // Inherited methods overridden:
     void run_op(ITensorPack &tensors, const Window &window, ::cl::CommandQueue &queue) override;
+
+private:
+    int32_t _depth{ 0 };
 };
 } // namespace kernels
 } // namespace opencl