[ROCm] Restore Inkling MTP backend parity

[AndreasKaratzas]

• Synchronize the backend-neutral AMD MTP orchestration with the NVIDIA implementation updated by PR [Model Runner V2][Spec Decode] Add multi-layer MTP speculator #48892.
• Select and construct only the checkpoint depth layers needed by the configured speculative-token count.
• Route each speculative step to its matching depth and ignore checkpoint weights for depths that were not constructed.
• Preserve AMD-specific kernels through the existing relative imports for model, normalization, attention, and short-convolution components.
• Keep the AMD and NVIDIA MTP source files byte-identical as required by the existing ROCm alignment contract.

PR #48892 added multi-layer MTP orchestration only to the NVIDIA copy and left the intentionally aligned AMD file stale. That omission causes the byte-alignment check to fail in the Inkling step. Inkling currently permits only one speculative token, so this restores the supported MTP=1 path without enabling unvalidated ROCm MTP>1 execution. The complete ROCm alignment test file passes locally.

[Fangzhou-Ai]

Thanks @AndreasKaratzas LGTM!

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[tjtanaa]

Can you share some validation results?

[AndreasKaratzas]

@tjtanaa Looks more or less the same to me.

Revision	GSM8K flexible	GSM8K strict	Accepted / drafted	Acceptance
Base 5c4fe4b	95.15%	93.63%	158,330 / 191,658	82.6107%
PR 7049a5d, run 1	96.44%	94.09%	153,960 / 186,256	82.6604%
PR 7049a5d, repeat	95.45%	93.40%	157,036 / 189,994	82.6531%

Draft acceptance rate is effectively unchanged: both head runs are approximately +0.04 - 0.05 percentage points versus base. GSM8K also remains within normal run-to-run variation.