COMPMID-1145: (API) Introduce prepare() stage (NEON/CL/GLES)

Change-Id: I5b46764f9c3154ec3e3b9c951cc9e6dfbcb81dfb
Reviewed-on: https://eu-gerrit-1.euhpc.arm.com/134255
Reviewed-by: Anthony Barbier <anthony.barbier@arm.com>
Tested-by: Jenkins <bsgcomp@arm.com>
Reviewed-by: Pablo Tello <pablo.tello@arm.com>
Reviewed-by: Michele DiGiorgio <michele.digiorgio@arm.com>
diff --git a/arm_compute/runtime/CL/functions/CLRNNLayer.h b/arm_compute/runtime/CL/functions/CLRNNLayer.h
index 9f239a9..ab7407d 100644
--- a/arm_compute/runtime/CL/functions/CLRNNLayer.h
+++ b/arm_compute/runtime/CL/functions/CLRNNLayer.h
@@ -69,6 +69,7 @@
 
     // Inherited methods overridden:
     void run() override;
+    void prepare() override;
 
 private:
     CLMemoryGroup              _memory_group;
@@ -80,6 +81,7 @@
     CLTensor                   _fully_connected_out;
     CLTensor                   _gemm_output;
     CLTensor                   _add_output;
+    bool                       _is_prepared;
 };
 }
 #endif /* __ARM_COMPUTE_CLRNN_LAYER_H__ */