cmd/objdump: add s390x GNU disasm support

cmd/objdump: add s390x GNU disasm support

This CL provides vendor support for s390x disassembler gnu syntax.
go get golang.org/x/arch@master
go mod tidy
go mod vendor

For #15255

Change-Id: Ia75fa515e7ea7d56913a28147c65650a7ab3062c
Reviewed-on: https://go-review.googlesource.com/c/go/+/581015
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Vishwanatha HD <vishwanatha.hd@ibm.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
Auto-Submit: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Bill O'Farrell <billotosyr@gmail.com>