cmd/compile: fold most repetitive operations to simplify riscv64 rules

cmd/compile: fold most repetitive operations to simplify riscv64 rules

Most of repetitive rules in riscv64 are simple, so that we can simplify and fold it with | without losting rules readability.

No change in the actual compiler code after running rulegen.

Change-Id: Id0bbfd93e63b49b7f66ecb62eb9440b4900c7938
Reviewed-on: https://go-review.googlesource.com/c/go/+/498455
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: M Zhuo <mzh@golangcn.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: M Zhuo <mzh@golangcn.org>