MLBEDSW-1499: Add MEAN operator

This commit adds support for the MEAN operator,
with some caveats.

Signed-off-by: Dwight Lidman <dwight.lidman@arm.com>
Change-Id: I165cb26cb5aefd68e70d2cfc68291ccf7b778921
diff --git a/ethosu/vela/npu_performance.py b/ethosu/vela/npu_performance.py
index 820c7d6..e315f1f 100644
--- a/ethosu/vela/npu_performance.py
+++ b/ethosu/vela/npu_performance.py
@@ -509,8 +509,7 @@
                 )
             else:
                 weight_tensor_shape = [
-                    primary_op.attrs["ksize"][1],
-                    primary_op.attrs["ksize"][2],
+                    *primary_op.get_kernel_size(),
                     1,
                     ifm_tensor_shape.depth,
                 ]