Enable TorchAO int4wo quantization tests on XPU

- Remove _int4wo_skip marker that restricted int4wo tests to CUDA only
- Add XPU-specific int4_packing_format='plain_int32' for Int4WeightOnlyConfig

Author: jiqing-feng

tests/models/testing_utils/quantization.py

@@ -818,6 +818,10 @@ class TorchAoConfigMixin:
     @staticmethod
     def _get_quant_config(config_name):
         config_cls = getattr(_torchao_quantization, config_name)
+        # TorchAO int4 quantization requires plain_int32 packing format on Intel XPU
+        if config_name == "Int4WeightOnlyConfig" and torch_device == "xpu":
+            return TorchAoConfig(config_cls(int4_packing_format="plain_int32"))
+
         return TorchAoConfig(config_cls())
 
     def _create_quantized_model(self, config_name, **extra_kwargs):
@@ -832,10 +836,6 @@ def _verify_if_layer_quantized(self, name, module, config_kwargs):
         assert isinstance(module, torch.nn.Linear), f"Layer {name} is not Linear, got {type(module)}"
 
 
-# int4wo requires CUDA-specific ops (_convert_weight_to_int4pack)
-_int4wo_skip = pytest.mark.skipif(torch_device != "cuda", reason="int4wo quantization requires CUDA")
-
-
 @is_torchao
 @require_accelerator
 @require_torchao_version_greater_or_equal("0.7.0")
@@ -861,7 +861,7 @@ class TorchAoTesterMixin(TorchAoConfigMixin, QuantizationTesterMixin):
     @pytest.mark.parametrize(
         "quant_type",
         [
-            pytest.param("int4wo", marks=_int4wo_skip),
+            "int4wo",
             "int8wo",
             "int8dq",
         ],
@@ -873,7 +873,7 @@ def test_torchao_quantization_num_parameters(self, quant_type):
     @pytest.mark.parametrize(
         "quant_type",
         [
-            pytest.param("int4wo", marks=_int4wo_skip),
+            "int4wo",
             "int8wo",
             "int8dq",
         ],
@@ -888,7 +888,7 @@ def test_torchao_quantization_memory_footprint(self, quant_type):
     @pytest.mark.parametrize(
         "quant_type",
         [
-            pytest.param("int4wo", marks=_int4wo_skip),
+            "int4wo",
             "int8wo",
             "int8dq",
         ],