[dev.ssa] cmd/compile: Add initial SSA configuration for PPC64

[dev.ssa] cmd/compile: Add initial SSA configuration for PPC64

This adds the initial SSA implementation for PPC64.
Builds golang and all.bash runs correctly.  Simple hello.go
builds but does not run.

Change-Id: I7cec211b934cd7a2dd75a6cdfaf9f71867063466
Reviewed-on: https://go-review.googlesource.com/24453
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>