simd(7): add missing aarch64 SIMD functions

Some of the string functions in contrib/arm-optimized routines are SIMD
enhanced which is not reflect on the simd(7) manpage. This commit
addresses that and introduces a new label A for functions enhanced with
the Arm ASIMD (Neon) extension.

Approved by: emaste
Reviewed by: fuz (GSoC mentor)
MFC to: stable/14
Sponsored by: Google LLC (GSoC 2024)
Differential Revision: https://reviews.freebsd.org/D45523

(cherry picked from commit 6c5ee6e55a35421248f914c4b00dc9ed555262fe)