Mostly indexed loads.  A few more LEA cases.

Change-Id: Idc1d447ed0dd6e906cd48e70307a95e77f61cf5f
Reviewed-on: https://go-review.googlesource.com/19172Reviewed-by: Todd Neal <todd@tneal.org>
Run-TryBot: Keith Randall <khr@golang.org>