SVE 256-bit Implementation of mxfp4 gemv kernel

[abhijain1204fujitsu]

Overview

This PR aims to add SVE 256 support for the ggml_gemv_mxfp4_4x4_q8_0 kernel found in profiling of gpt-oss-20b MoE model.

Additional information

GPT-OSS-20B SVE256 Performance

(Taken on Graviton3e)

Task	Threads	NEON	SVE 256	Improvement (%)
PP128	4	25.71	29.30	13.96
TG128	4	20.84	23.39	12.24
PP128	8	51.09	58.19	13.90
TG128	8	37.94	42.01	10.73
PP128	16	100.40	113.92	13.47
TG128	16	61.35	65.86	7.35
PP128	32	188.67	213.06	12.93
TG128	32	73.99	76.31	3.14

Perplexity:

Metric	NEON	SVE
Final Estimate PPL	297.7341 ± 18.27793	297.7341 ± 18.27793

Requirements

• I have read and agree with the contributing guidelines
• AI usage disclosure: No

Co Authors: @anubhavfujitsu

[ggml-gh-bot]

Hi @abhijain1204fujitsu, thanks for your contribution!

Per our contribution guidelines, the automated PR checker found the following issue(s) that need your attention:

• Maintainers cannot push to this PR: Please enable Allow edits by maintainers. If this PR comes from an organization-owned fork, that option is not available on GitHub; please re-open the PR from a fork owned by your personal account.

---

Please note that maintainers reserve the right to make final decisions on PRs. If you believe there is a mistake, please comment below.

[abhijain1204fujitsu]

@ggerganov, @Alcpz
Kindly support to review the PR