cmd/compile: intrinsify runtime/internal/atomic.{And,Or}{8,} on RISCV64

The 32 bit versions are easily implement with a single instruction, while the
8 bit versions require a bit more effort but use the same atomic instructions
via rewrite rules.

Change-Id: I42e8d457b239c8f75e39a8e282fc88c1bb292a99
Reviewed-on: https://go-review.googlesource.com/c/go/+/268098


Trust: Joel Sing <joel@sing.id.au>
Run-TryBot: Joel Sing <joel@sing.id.au>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>