Fix XNNPACK handling of negative permute dims (#14169)

### Summary
Fix handling of negative dims in permute ops on XNNPACK. They currently
fail to lower. This bug was surfaced by the backend operator test suite.

### Test plan
I've added a test to cover negative dims in permute.

Author: GregoryComer

backends/xnnpack/operators/op_permute.py

@@ -44,14 +44,21 @@ def define_node(
         self.define_nodes_tensor_inputs_outputs(node, xnn_graph, vals_to_ids)
 
         # input
-        input_id = vals_to_ids[get_input_node(node, 0)]
+        input_node = get_input_node(node, 0)
+        input_id = vals_to_ids[input_node]
 
         # output
         output_id = vals_to_ids[node]
 
         # permutation
+        input_rank = input_node.meta["val"].dim()
         permute_order = cast(List[int], node.args[1])
 
+        # Handle negative dimensions by converting them to positive indices
+        permute_order = [
+            (dim + input_rank) if dim < 0 else dim for dim in permute_order
+        ]
+
         # change permute order if under channels last
         is_channels_last = node.meta.get(
             ChannelsLastTaggedReshapePass.XNN_NHWC_NODE, False

backends/xnnpack/test/ops/test_permute.py

@@ -55,6 +55,20 @@ def test_fp32_permute(self):
         inputs = (torch.randn(1, 1, 4, 4),)
         self._test_permute(inputs)
 
+    def test_fp32_permute_negative_dim(self):
+        inputs = (torch.randn(1, 1, 4, 4),)
+        (
+            Tester(self.Permute([0, -2, -1, 1]), inputs)
+            .export()
+            .check_count({"torch.ops.aten.permute.default": 1})
+            .to_edge_transform_and_lower()
+            .check_count({"torch.ops.higher_order.executorch_call_delegate": 1})
+            .check_not(["executorch_exir_dialects_edge__ops_aten_permute_copy_default"])
+            .to_executorch()
+            .serialize()
+            .run_method_and_compare_outputs()
+        )
+
     def test_fp32_permute_copy(self):
         inputs = (torch.randn(1, 1, 4, 4),)
         (