[Model] Support SDPA attention for Molmo vision backbone

[Isotr0py]

FILL IN THE PR DESCRIPTION HERE

FIX #xxxx (link existing issues this PR will resolve)

• Add sdpa implementation to Molmo ViT attention
• Clean up ViT attention backend selection for Molmo and Qwen2-VL

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[github-actions]

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[DarkLight1337]

Thanks for adding this and the cleanup!