share/man/man7/simd.7: add forgotten aarch64 string functions

I previously forgot to mention these as they are set up through
contrib/arm-optimized/routines/string.

Tested by: developers@, exp-run
Approved by: mjg
MFC after: 1 month
MFC to: stable/14
PR: 275785

(cherry picked from commit 6fdcb85b1c10fb7a7f61323e52ee251cc48fd60e)