update xpu quant usage

Signed-off-by: Kaihui-intel <kaihui.tang@intel.com>

docs/source/3x/transformers_like_api.md

@@ -208,6 +208,7 @@ python run_generation_gpu_woq.py --woq --benchmark --model save_dir
 >Note:
 > * Saving quantized model should be executed before the optimize_transformers function is called.
 > * The optimize_transformers function is designed to optimize transformer-based models within frontend Python modules, with a particular focus on Large Language Models (LLMs). It provides optimizations for both model-wise and content-generation-wise. The detail of `optimize_transformers`, please refer to [the link](https://github.com/intel/intel-extension-for-pytorch/blob/xpu-main/docs/tutorials/llm/llm_optimize_transformers.md).
+>* The quantization process is performed on the CPU accelerator by default. Users can override this setting by specifying the environment variable `INC_TARGET_DEVICE`. Usage on bash: ```export INC_TARGET_DEVICE=xpu```.
 
 ## Examples
 

examples/3.x_api/pytorch/nlp/huggingface_models/language-modeling/quantization/transformers/weight_only/text-generation/README.md

@@ -103,6 +103,7 @@ python run_generate_cpu_woq.py \
 > 1.  default search algorithm is beam search with num_beams = 1.
 > 2. [ipex.optimize_transformers](https://github.com/intel/intel-extension-for-pytorch/blob/v2.1.10%2Bxpu/docs/tutorials/llm/llm_optimize_transformers.md) Support for the optimized inference of model types "gptj," "mistral," "qwen," and "llama" to achieve high performance and accuracy. Ensure accurate inference for other model types as well.
 > 3. We provide compression technologies `WeightOnlyQuant` with `Rtn/GPTQ/AutoRound` algorithms and `load_in_4bit` and `load_in_8bit` work on intel GPU device.
+> 4. The quantization process is performed on the CPU accelerator by default. Users can override this setting by specifying the environment variable `INC_TARGET_DEVICE`. Usage on bash: ```export INC_TARGET_DEVICE=xpu```.
 
 ## Prerequisite​
 ### Dependencies

neural_compressor/transformers/quantization/utils.py

@@ -347,14 +347,17 @@ def run_fn_for_autoround(model, dataloader):
 
 
 def convert_to_quantized_model(model, config, device="cpu"):
+
     if device == "xpu" or device == torch.device("xpu"):
         import intel_extension_for_pytorch
 
         assert hasattr(torch, "xpu") and torch.xpu.is_available(), "There is no xpu device in this system!"
-        os.environ["INC_TARGET_DEVICE"] = "cpu"
-        logger.info(
-            "Set the environment variable INC_TARGET_DEVICE='cpu' to ensure the quantization process occurs on the CPU."
-        )
+        if "INC_TARGET_DEVICE" not in os.environ:
+            os.environ["INC_TARGET_DEVICE"] = "cpu"
+            logger.info(
+                "Set the environment variable INC_TARGET_DEVICE='cpu'"
+                " to ensure the quantization process occurs on the CPU."
+            )
 
     orig_dtype = torch.float32
     for param in model.parameters():