Revert "Revert "MLBEDSW-3645 4D class for op ifm/ofm shapes""

This reverts commit df0a5905177f3a1b836076bc3f9f39b2e86f1794.

Reason for revert: <INSERT REASONING HERE>

Change-Id: I891c66fb29db9d25e942947e8d1c29a10610de51
diff --git a/ethosu/vela/test/test_graph_optimiser.py b/ethosu/vela/test/test_graph_optimiser.py
index 4537741..7fdc4bd 100644
--- a/ethosu/vela/test/test_graph_optimiser.py
+++ b/ethosu/vela/test/test_graph_optimiser.py
@@ -21,6 +21,7 @@
 from ethosu.vela.graph_optimiser import convert_batched_fc_shape
 from ethosu.vela.operation import Op
 from ethosu.vela.tensor import create_const_tensor
+from ethosu.vela.tensor import Shape4D
 from ethosu.vela.tensor import Tensor
 from ethosu.vela.test import testutil
 
@@ -35,8 +36,8 @@
 
     ifm.consumer_list.append(op)
 
-    op.ifm_shapes.append([4, 1, 1, 8])
-    op.ofm_shapes.append([4, 1, 1, 8])
+    op.ifm_shapes.append(Shape4D([4, 1, 1, 8]))
+    op.ofm_shapes.append(Shape4D([4, 1, 1, 8]))
 
     prev_op = op.clone()
     prev_op.ifm_shapes = op.ifm_shapes