Fix gpt-oss-20b with mxfp4 support for Xeon (#27782)

python/sglang/srt/layers/quantization/__init__.py

@@ -55,6 +55,7 @@ from sglang.srt.layers.quantization.w8a8_int8 import W8A8Int8Config
 from sglang.srt.platforms import current_platform
 from sglang.srt.utils import (
     cpu_has_amx_support,
+    is_cpu,
     is_cuda,
     is_hip,
     is_mps,
@@ -99,7 +100,7 @@ BASE_QUANTIZATION_METHODS: Dict[str, Type[QuantizationConfig]] = {
 }
 
 
-if is_cuda() or (_is_mxfp_supported and is_hip()):
+if is_cpu() or is_cuda() or (_is_mxfp_supported and is_hip()):
     BASE_QUANTIZATION_METHODS.update(
         {
             "mxfp4": Mxfp4Config,
@@ -130,6 +131,7 @@ CPU_QUANTIZATION_METHODS = {
     "compressed-tensors": CompressedTensorsConfig,
     "awq": AWQCPUConfig,
     "gptq": CPUGPTQConfig,
+    "mxfp4": Mxfp4Config,
 }
 
 QUANTIZATION_METHODS = {**BASE_QUANTIZATION_METHODS}