COMPMID-3957: Deprecate CV functions in CL backend.

Change-Id: Ic3deac8d6ce128312f49aa1ddf9f508d05d1b7a2
Signed-off-by: morgolock <pablo.tello@arm.com>
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/4368
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
Reviewed-by: Sheri Zhang <sheri.zhang@arm.com>
Tested-by: Arm Jenkins <bsgcomp@arm.com>
diff --git a/arm_compute/runtime/CL/functions/CLHistogram.h b/arm_compute/runtime/CL/functions/CLHistogram.h
index 164bd0a..b45a79e 100644
--- a/arm_compute/runtime/CL/functions/CLHistogram.h
+++ b/arm_compute/runtime/CL/functions/CLHistogram.h
@@ -37,6 +37,8 @@
  *  -# @ref CLHistogramKernel
  *  -# @ref CLHistogramBorderKernel
  *
+ * @deprecated This function is deprecated and is intended to be removed in 21.05 release
+ *
  */
 class CLHistogram : public IFunction
 {