Rework divisor calculation for AVGPOOL2D

Previous code assumed symmetric padding when calculating the divisor for
the average pool, and had issues with extra padding.
The padding now follows the definition from the specification. Extra
padding to the right/bottom is ignored when calculating the average pool
divisor.

Change-Id: Ib05e2346c6e9d55b6fef5294322e58ee18ef4928
diff --git a/reference_model/src/ops/tensor_ops.h b/reference_model/src/ops/tensor_ops.h
index 2174d62..05b1ca1 100644
--- a/reference_model/src/ops/tensor_ops.h
+++ b/reference_model/src/ops/tensor_ops.h
@@ -73,7 +73,7 @@
 
 protected:
     // return a 1D [N] tensor that describes a how many valid elements covered in the input space
-    ETensor1<int32_t> calculate_div_map_1d(int in_size, int out_size, int kernel_size, int stride);
+    ETensor1<int32_t> calculate_div_map_1d(int in_size, int out_size, int kernel_size, int stride, int32_t padding_left, int32_t padding_right);
 };
 
 template <DType InDtype, DType WeightDtype>