[dev.link] cmd/link: support new dodata for PPC64

[dev.link] cmd/link: support new dodata for PPC64

Add linux/{ppc64,ppc64le} and aix/ppc64 arch support for the new
dodata() phase.

This completes the picture in terms of architecture support for the
new dodata(), but to be safe this patch leaves the command line flag
in place there are problems on the builders (especially given that we
have a dead aix-ppc64 builder).

Change-Id: I78da615c3b540d8925ed7b3226e199280eb7451d
Reviewed-on: https://go-review.googlesource.com/c/go/+/229983
Reviewed-by: Cherry Zhang <cherryyz@google.com>