internal/cpu: don't run SSE3 disable test if GOAMD64>1

internal/cpu: don't run SSE3 disable test if GOAMD64>1

That feature can't be disabled if the microarchitectural version
requires it.

Change-Id: Iad8aaa8089d2f023e9ae5044c6da33224499f09b
Reviewed-on: https://go-review.googlesource.com/c/go/+/392994
Run-TryBot: Keith Randall <khr@golang.org>
Trust: Keith Randall <khr@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Martin Möhrmann <martin@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>