.travis.yml: Add a KVM-only s390x job

.travis.yml: Add a KVM-only s390x job

Add a job to build QEMU on s390x with TCG disabled, so
this configuration won't bitrot over time.

This job is quick, running check-unit: Ran for 5 min 30 sec
https://travis-ci.org/github/philmd/qemu/jobs/665456423

Acked-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20200322154015.25358-1-philmd@redhat.com>
Message-Id: <20200323161514.23952-12-alex.bennee@linaro.org>