Add Flash decoding kernel ROCm

[mht-sharma]

What does this PR do?

As per title!

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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• Did you write any new necessary tests?

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[danieldk]

Looks good to me, but would be nice if we could get a CI run.

[mht-sharma]

Looks good to me, but would be nice if we could get a CI run.

@danieldk CI runners for rocm are currently deactivated due to security issues.