share/man/man7/simd.7: document SIMD-enhanced aarch64 functions

This documents all the newly ported SIMD-enhanced string functions
for the aarch64 platform.

Reviewed by: fuz, emaste
Sponsored by: Google LLC (GSoC 2024)
Relnotes: yes
PR: 281175
Differential Revision: https://reviews.freebsd.org/D46452