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/CLDepthwiseConvolutionLayer.h b/arm_compute/runtime/CL/functions/CLDepthwiseConvolutionLayer.h
index b1eb4b9..229fb24 100644
--- a/arm_compute/runtime/CL/functions/CLDepthwiseConvolutionLayer.h
+++ b/arm_compute/runtime/CL/functions/CLDepthwiseConvolutionLayer.h
@@ -140,6 +140,7 @@
 
     // Inherited methods overriden:
     void run() override;
+    void prepare() override;
 
 private:
     CLDepthwiseIm2ColKernel                   _im2col_kernel;
@@ -153,7 +154,7 @@
     CLTensor                                  _weights_reshaped;
     CLTensor                                  _v2mm_output;
     CLTensor                                  _output_reshaped;
-    bool                                      _is_first_run;
+    bool                                      _is_prepared;
     bool                                      _is_quantized;
     const ICLTensor                          *_original_weights;
 };