Mostly copied from ARM port, with instruction names and Prog fields
adjusted, and 64-bit int ops added. Not complete.

Fib compiles and runs correctly.

Change-Id: Id3ecb0d4b571200a035344b3e8e4408769f76221
Reviewed-on: https://go-review.googlesource.com/25130Reviewed-by: David Chase <drchase@google.com>
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>