feat(neon): add AArch32 compatibility for FMA intrinsics in neon_mathfun.h

[Abandon-ht]

The vfmaq_f32/vfmsq_f32 intrinsics are only available on AArch64.
To support ARM 32-bit (AArch32) targets, replace direct usage with
portable macros that fall back to vmlaq_f32/vmlsq_f32 on 32-bit NEON.

This enables successful compilation on armeabi-v7a while preserving
FMA performance on AArch64. All math functions (log, exp, sin, cos, etc.)
retain identical behavior and accuracy.

[tencent-adm]

Thank you for your submission, we really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.88%. Comparing base (3ab4b58) to head (5b93449).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6393      +/-   ##
==========================================
- Coverage   95.89%   95.88%   -0.01%     
==========================================
  Files         841      841              
  Lines      266338   266338              
==========================================
- Hits       255402   255379      -23     
- Misses      10936    10959      +23     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[github-actions]

The binary size change of libncnn.so (bytes)

architecture	base size	pr size	difference
x86_64	15212648	15212648	0 😘
armhf	6206656	6206656	0 😘
aarch64	9524368	9524560	+192 ⚠️

[Copilot]

Copilot encountered an error and was unable to review this pull request. You can try again by re-requesting a review.

[Copilot]

Pull Request Overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[nihui]

Thanks for your contribution !

[nihui]

Thanks for your contribution !