Only added lines are moving amd64 and x86's ginsnop functions from
gsubr.go to ggen.go to match other architectures, so all of the
gsubr.go files can go away.

Change-Id: Ib2292460c155ae6d9dcf5c9801f178031d8eea7a
Reviewed-on: https://go-review.googlesource.com/29240
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dave Cheney <dave@cheney.net>