riscv/atomic: Provide some additional aliases

These are already available and having them defined helps keep the KASAN
atomic(9) interceptors uniform.

Reviewed by: mhorne
MFC after: 1 week
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D58680

(cherry picked from commit 4f87828402912a7e451fdbe53161c68faa489128)