cmd/internal: allow ADDE to work with memory location on s390x

Originally on s390x, ADDE does not work when adding numbers from a memory location.
For example: ADDE (R3), R4 will result in a failure.

Since ADDC, ADD and ADDW already supports adding from memory location,
let's support that for ADDE as well.

Change-Id: I7cbe112ea154733a621b948c6a21bbee63fb0c62
Reviewed-on: https://go-review.googlesource.com/c/go/+/229304


Reviewed-by: Michael Munday <mike.munday@ibm.com>
Run-TryBot: Michael Munday <mike.munday@ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>