cmd/compile: use separate addressing modes pass for s390x

[randall77]

Split off from #36468 .

We now have a separate addressing modes pass, which produces the *idxX operations on x86. s390x could also take advantage of this pass, which would reduce the number of rewrite rules that need to be specified.

@mundaym

[gopherbot]

Change https://golang.org/cl/250958 mentions this issue: cmd/compile: use addressing modes pass on s390x