COMPMID-556: Static helper function for getting gws from window.

Change-Id: I3e47385b2f7a7977c2c61272f2fb30e800f39406
Reviewed-on: http://mpd-gerrit.cambridge.arm.com/93429
Tested-by: Kaizen <jeremy.johnson+kaizengerrit@arm.com>
Reviewed-by: Anthony Barbier <anthony.barbier@arm.com>
diff --git a/arm_compute/core/CL/ICLKernel.h b/arm_compute/core/CL/ICLKernel.h
index 9119940..a1bc3eb 100644
--- a/arm_compute/core/CL/ICLKernel.h
+++ b/arm_compute/core/CL/ICLKernel.h
@@ -180,6 +180,13 @@
      * @return The maximum workgroup size value.
      */
     size_t get_max_workgroup_size();
+    /** Get the global work size given an execution window
+     *
+     * @param[in] window Execution window
+     *
+     * @return Global work size of the given execution window
+     */
+    static cl::NDRange gws_from_window(const Window &window);
 
 private:
     /** Add the passed array's parameters to the object's kernel's arguments starting from the index idx.