cmd/internal/obj/arm64: add NOOP description in Go assembly syntax
cmd/internal/obj/arm64: add NOOP description in Go assembly syntax

This Patch describes NOOP in Go assembly syntax and gives Go assembly
example and corresponding GNU assembly example.

Change-Id: I9db659cc5e3dc6b1f1450f2064255af8872d4b1c
Reviewed-on: https://go-review.googlesource.com/c/go/+/207400
Run-TryBot: eric fang <68c7b5ebe4a86ef7e52157f5950041656bf82310@arm.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Cherry Zhang <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>

golang/go,nawawi/go,golang/go,akutz/go,akutz/go,nawawi/go,nawawi/go,CAFxX/go,nawawi/go,cloudflare/go,akutz/go,nawawi/go,golang/go,nawawi/go,CAFxX/go,cloudflare/go,nawawi/go,akutz/go,akutz/go,CAFxX/go,akutz/go,akutz/go,cloudflare/go,golang/go,akutz/go,golang/go,cloudflare/go,nawawi/go,golang/go,cloudflare/go,cloudflare/go,CAFxX/go,CAFxX/go,cloudflare/go,CAFxX/go,CAFxX/go,golang/go,golang/go,cloudflare/go,CAFxX/go