riscv: Add implementations of atomic_testand(set|clear)_(32|64|long)

These use amoor and amoand rather than a loop.

Also define atomic_testandset_acq_(64|long) using amoor.aq.

Reviewed by: mhorne, kib
Sponsored by: AFRL, DARPA
Differential Revision: https://reviews.freebsd.org/D47627