Update on "[quant] Move the order of x86 engine to avoid changing the…

… default qengine"

since the default qengine is the last element of the engine in supported_engines list, adding x86 qengine in the end of the list changes the default quantized engine as well. this PR will be a short term fix to revert the changes. We have an issue here to track the proper fix: #86404

[ghstack-poisoned]

torch/ao/quantization/qconfig_mapping.py

@@ -120,25 +120,25 @@ def _get_default_qconfig_mapping(is_qat: bool, backend: str, version: int) -> QC
 
     return qconfig_mapping
 
-def get_default_qconfig_mapping(backend="x86", version=0) -> QConfigMapping:
+def get_default_qconfig_mapping(backend="fbgemm", version=0) -> QConfigMapping:
     """
     Return the default QConfigMapping for post training quantization.
 
     Args:
       * ``backend`` : the quantization backend for the default qconfig mapping, should be
-         one of ["x86" (default), "fbgemm", "qnnpack", "onednn"]
+         one of ["x86", "fbgemm" (default), "qnnpack", "onednn"]
       * ``version`` : the version for the default qconfig mapping
     """
     # TODO: add assert for backend choices
     return _get_default_qconfig_mapping(False, backend, version)
 
-def get_default_qat_qconfig_mapping(backend="x86", version=1) -> QConfigMapping:
+def get_default_qat_qconfig_mapping(backend="fbgemm", version=1) -> QConfigMapping:
     """
     Return the default QConfigMapping for quantization aware training.
 
     Args:
       * ``backend`` : the quantization backend for the default qconfig mapping, should be
-         one of ["x86" (default), "fbgemm", "qnnpack", "onednn"]
+         one of ["x86", "fbgemm" (default), "qnnpack", "onednn"]
       * ``version`` : the version for the default qconfig mapping
     """
     return _get_default_qconfig_mapping(True, backend, version)