ciflow/xpu/186797: [XPU] Fix test_autotune_gemm_choice_validation for mm_plus_mm, add TODO

Per Claude code review: removing the Triton mm_plus_mm template on XPU

broke test_autotune_gemm_choice_validation which asserts TritonTemplateCaller

is always present when max_autotune=True. Guard the assertion for the

mm_plus_mm+XPU case.

Also add TODO(#184490) in mm_plus_mm.py to mark the XPU guard as temporary

— it should be lifted once the underlying Triton codegen accuracy bug is

fixed so XPU can benefit from the fused template perf.

Co-authored-by: Copilot [email protected]