[CI/Build] Skip encoder-decoder models on AMD

[zhewenl]

Purpose

See more details in #27442. Encoder-decoder models (Whisper, T5, BART, vision-language models) fail on AMD ROCm with NotImplementedError because all ROCm-specific attention backends only support decoder-only models.

Therefore, all the tests using these models will fail on AMD CI(example), mainly in Entrypoints Integration Test (API Server) and Entrypoints Integration Test (Pooling):

NotImplementedError: Encoder self-attention and encoder/decoder cross-attention
are not implemented for TritonAttentionImpl

In this PR:

• Tests that contain BOTH encoder and decoder models use @pytest.mark.encoder_decoder on specific tests/variants; also fixed some tests not using parametrized fixtures.
• Tests that contain ONLY encoder models are skipped entirely at the CI level in test-amd.yaml.
• Ad-hoc patches tests can not skip/add decorator to skip easily by patching the simple logic to skip on ROCm platform.

Test Plan

CI: https://buildkite.com/vllm/amd-ci/builds/1020

[ywang96]

cc @russellb @robertgshaw2-redhat

AFAIR we have reached an agreement that the only enc-dec model we're going to support in V1 is whisper, so we should deprecate other models.

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[zhewenl]

@DarkLight1337 Thanks for catching this! Updated list and relevant tests

[zhewenl]

We will hold this PR as #28346, #28376 attempts to fix encoder-decoder on ROCM