add non packed fp8 format for Triton attn decode

[scxiao]

What does this PR do?

Fixes # (issue).

Current implementation for fp8 uses a packed fp8 format, which needs additional unpack steps for dequantization from fp8 to bf16. This PR is to add the support of the non-packed fp8 format for Triton attn decode, it is about 20% to 30% faster than packed format on AMD MI350.

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