[XPU] Automatically detect target platform as XPU in build. (#37634)

Signed-off-by: huanxing <huanxing.shen@intel.com>

setup.py

@@ -54,6 +54,9 @@ elif sys.platform.startswith("linux") and os.getenv("VLLM_TARGET_DEVICE") is Non
     if torch.version.hip is not None:
         VLLM_TARGET_DEVICE = "rocm"
         logger.info("Auto-detected ROCm")
+    elif torch.version.xpu is not None:
+        VLLM_TARGET_DEVICE = "xpu"
+        logger.info("Auto-detected XPU")
     elif torch.version.cuda is not None:
         VLLM_TARGET_DEVICE = "cuda"
         logger.info("Auto-detected CUDA")