lib/libc/aarch64/string: add bcopy & bzero wrapper

This patch enabled usage of SIMD enhanced functions to implement
bcopy and bzero.

Tested by: fuz (exprun)
Reviewed by: fuz, emaste
Sponsored by: Google LLC (GSoC 2024)
PR: 281175
Differential Revision: https://reviews.freebsd.org/D46459