hexagon: minor refresh for HMX FA and MM (llama/23796)

hexagon: minor refresh for HMX FA and MM (llama/23796)

* hex-fa: clean up qf32/fp32 handling and stride handling

* hex-fa: fix corner case fp NAN issues that were cause bad output from gemma4 on v79

* hex-fa: vectorize leftover handling

* hex-fa: avoid HVX fallback during token gen HMX has more FP16 compute capacity

* hmx-mm: remove dead code

* hmx-mm: use fastdiv in x4x2 dequant

* hmx-mm: sandwich dequant and scatter to improve perf

* hmx-mm: fixed rebase conflicts

* hmx-mm: further improve weight dequant by doing early type dispatch and precomputing fastdiv

* hmx-mm: an even earlier dispatch for per-type dequant

* hmx-mm: dequant linear types like q4_0 and q4_1 without the LUTs

This is a bit faster than LUT.

* hex-cmake: one more tweak for lto

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Co-authored-by: Trivikram Reddy <redacted>