hexagon: optimize HMX matmul operations

[chraac]

Overview

This pull request refactors several matrix multiplication and data handling routines in ggml-hexagon/htp/hmx-matmul-ops.c to improve type safety, consistency, and code clarity. The main changes involve standardizing loop counters and size-related variables to use size_t instead of int, updating function signatures accordingly, and simplifying tile indexing logic. Additionally, the initialization of column scales is made more consistent, and some redundant or legacy code paths are removed.

Type safety and consistency improvements:

• Changed loop counters and size-related variables from int to size_t across multiple functions (e.g., core_dot_chunk_fp16, core_mma_chunk_fp16, transfer_output_chunk_fp16_to_fp32) and updated related calculations and function signatures for better type safety and to prevent integer overflow issues. [1] [2] [3] [4] [5]
• Updated function signatures and local variable declarations to consistently use const size_t for sizes and counts, improving code clarity and reducing potential bugs from type mismatches. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]

Additional information

Tested with Qwen3.5-2b-q4, works well

Requirements

• I have read and agree with the contributing guidelines
• AI usage disclosure: YES, for commit log and PR descriptions

[chraac]

Key change: move scale and bias initialization out of the loop instead of reinitializing the same scale each iteration, to reduces some HMX register setup.

[chraac]

Potential follow-up: reuse this scale for quant-block scaling to avoid the dequantization vmpy, at the cost of extra VTCM cache for scale storage...

[max-krasnyansky]

@chraac
Sorry for the delay on this. We have a couple of decent size changes coming in this area (op request batching/buffer management and HMX optimizations).
We'll probably merge that stuff first (hopefully by end of this week), then I'm going to work with you to rebase/update/merge things on top.

[chraac]

We'll probably merge that stuff first (hopefully by end of this week), then I'm going to work with you to rebase/update/merge things on top.

Np, lets wait for your PR merged first, then redo this one based on that.

[max-krasnyansky]

@chraac here is that PR that I mentioned #21705
There are more HMX specific updates coming on top shortly.