Mnemonics for these instructions were added to the assembler in
CL 159357.

Change-Id: Ie11c45ecc9cead9a8850fcc929b0211cfd980fe5
Reviewed-on: https://go-review.googlesource.com/c/go/+/160157
Run-TryBot: Michael Munday <mike.munday@ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>