ppc64/ppc64asm: first round of fixes

- make test pass on 32-bit systems
- make test skip objdump when objdump not available,
  like in the other architecture tests
- expose plan9Syntax as GoSyntax

Change-Id: I8b1bb7cc4a07c6bd8a4eb0569553cb47773fb2a4
Reviewed-on: https://go-review.googlesource.com/30934
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
5 files changed