fix(trtllm): restrict routed-MoE backends to supported architectures (release port for #4107)

[kahyunnam]

Description

Release-specific port of #4177 onto release-v0.6.16 for #4107.

On SM12x (Spark, RTX Pro 6000), TRTLLM routed-MoE backends were incorrectly
claiming support (arch >= 100) and then dispatching sm100f/sm103a cubins,
causing RuntimeError: Error occurred when running GEMM! or segfaults in
test_split_fused_moe_kernel_vs_reference.

Changes

• csrc/trtllm_batched_gemm_runner.cu: Replace per-SM if-chains with
  isArchCompatible(); reject unknown cubin families; guard Sm107a behind
  #ifdef TLLM_RUBIN_FEATURES (only exists in the Rubin cubin pin's headers).
• csrc/trtllm_gemm_runner.cu: Same arch filter for the plain GEMM runner
  (previously had no arch filtering at all).
• flashinfer/fused_moe/api.py: Tighten Trtllm*Config.supported() from
  arch >= 100 to explicit allowlists _TRTLLM_ROUTED_ARCHS = (100, 103, 107)
  and _TRTLLM_ROUTED_FP8_ARCHS = (100, 103).
• tests/moe_ep/test_split_fused_moe_kernel_vs_reference.py: Gate GPU tests
  on config_cls.supported(arch); add CPU contract tests + SM120 regression guard.

Release-specific notes

• Includes sm107 in the allowlist (unlike the rebased fix(trtllm): restrict TRT-LLM routed-MoE and GEMM backends to supported architectures #4177 for main, which
  will drop 107 after the Adds SM107 support #4122 revert).
• Sm107a enum case is gated behind TLLM_RUBIN_FEATURES, matching the existing
  release pattern from Adds SM107 support #4122/Split trtllm-gen cubin pins per arch #4191. Verified against the actual pinned headers:
  the default BMM/GEMM pins do not define Sm107a; only the Rubin pins do.

Verification

• CPU tests: 36 passed, 2 skipped (test_split_fused_moe_kernel_vs_reference.py)
• Backend claims: sm120/sm121 now fall back to Cutlass only (no Trtllm* backends)
• Compile: isArchCompatible() builds cleanly against both default and Rubin BMM
  export headers; ported batched runner compiles against default pin

Related

• Fixes [bug][v0.6.16] test_split_fused_moe_kernel_vs_reference error at /workspace/flashinfer/csrc/trtllm_batched_gemm_runner.cu:305: Error occurred when running GEMM! #4107
• Upstream PR: fix(trtllm): restrict TRT-LLM routed-MoE and GEMM backends to supported architectures #4177 (targets main, has merge conflicts)
• Cherry-pick source commit on main: not yet merged

Pre-existing issue (not in scope)

#4213 on release references options.mDtypeSfC, which does not exist in the
default BMM cubin pin's headers (only in the Rubin pin). This is a separate
release-only compile issue on the non-Rubin module, predating this port.

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[mhoqueanik]

#4177 started efforts to addresss the issue in restricting TRT-LLM routed-MoE and GEMM backends to supported architectures.