Adding cases for ppc64,ppc64le to the codegen tests
where appropriate.

Change-Id: Idf8cbe88a4ab4406a4ef1ea777bd15a58b68f3ed
Reviewed-on: https://go-review.googlesource.com/c/142557


Run-TryBot: Lynn Boger <laboger@linux.vnet.ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>