Arm backend: Keep DeepSeek FP8 on xlarge path

[bdemirb]

Keep the DeepSeek-R1-Distill-Qwen-1.5B FP8 layer tests on the existing generic xlarge TOSA and VKML model suites.

This drops the dedicated DeepSeek job wiring added in the previous patchset and follows the existing Arm backend model for memory-heavy coverage: smaller cases stay in the normal shard and heavy cases run through the serialised xlarge path.

That keeps the FP8 coverage in CI without introducing DeepSeek-specific test entrypoints or workflow jobs.

cc @digantdesai @freddan80 @per @zingo @oscarandersson8218 @mansnils @Sebastian-Larsson @robell @rascani

[pytorch-bot]

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• [ALERT ONLY] - System Maintenance

❌ 7 New Failures, 1 Unrelated Failure

As of commit 1750c29 with merge base 8702327 ():

NEW FAILURES - The following jobs have failed:

• pull / unittest-nxp-neutron / linux-job (gh)
  ../../dev/ir/converter/node_converter/test_upsample_bilinear2d.py::TestUpsampleBilinear2D::test__not_align_corners__output_size[batch=2,
• trunk / test-custom-ops-macos (cmake) / macos-job (gh)
  Failed to resolve action download info. Error: Service Unavailable
• trunk / test-huggingface-transformers-macos (llama3.2-1b|coreml_fp32_gpu|--quantize) / macos-job (gh)
  ##[error]fatal: unable to access 'https://github.com/google/flatbuffers.git/': Failed to connect to github.com port 443 after 15510 ms: Couldn't connect to server
• trunk / test-llama-runner-mac (fp32, mps) / macos-job (gh)
  Failed to resolve action download info. Error: Service Unavailable
• trunk / test-models-macos-coreml (edsr) / macos-job (gh)
  Failed to resolve action download info. Error: Service Unavailable
• trunk / test-models-macos-coreml (emformer_transcribe) / macos-job (gh)
  Failed to resolve action download info. Error: Service Unavailable
• trunk / test-models-macos-coreml (mv3) / macos-job (gh)
  Failed to resolve action download info. Error: Service Unavailable

FLAKY - The following job failed but was likely due to flakiness present on trunk:

• trunk / test-models-macos-cpu (llama3_2_vision_encoder, portable) / macos-job (gh) (detected as infra flaky with no log or failing log classifier)

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[bdemirb]

@pytorchbot label "partner: arm"

[bdemirb]

@pytorchbot label "release notes: arm"

[zingo]

Just a note: test_pytest_models_*_xlarge don't seem to be run on GitHub is that on purpos?
e.g. is the model too large?