runtime: improve the annotation of debugCallV2 for arm64
runtime: improve the annotation of debugCallV2 for arm64

This CL improves the annotation documentation of the debugCallV2 function
for arm64.

Change-Id: Icc2b52063cf4fe779071039d6a3bca1951108eb0
Reviewed-on: https://go-review.googlesource.com/c/go/+/402514
Reviewed-by: Cherry Mui <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>
Run-TryBot: Eric Fang <68c7b5ebe4a86ef7e52157f5950041656bf82310@arm.com>
Reviewed-by: Alessandro Arzilli <e26d9aa77fb315046750e4f7a9c5cd199e338f92@gmail.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: David Chase <ae171625adc8645b8b79b7e405a6da5aba5341e0@google.com>

golang/go,nawawi/go,nawawi/go,nawawi/go,golang/go,nawawi/go,golang/go,golang/go,nawawi/go,golang/go,nawawi/go,golang/go,nawawi/go,golang/go,golang/go,nawawi/go