cmd/compile: fold address calculations into CMPload[const] ops

Makes go binary smaller by 0.2%.

I noticed this in autogenerated equal methods, and there are
probably a lot of those.

Change-Id: I4e04eb3653fbceb9dd6a4eee97ceab1fa4d10b72
Reviewed-on: https://go-review.googlesource.com/135379


Reviewed-by: Ilya Tocar <ilya.tocar@intel.com>