s390x: firq: floating interrupt test

We had a KVM BUG fixed by kernel commit a3e03bc1368c ("KVM: s390: index
kvm->arch.idle_mask by vcpu_idx"), whereby a floating interrupt might get
stuck forever because a CPU in the wait state would not get woken up.

The issue can be triggered when CPUs are created in a nonlinear fashion,
such that the CPU address ("core-id") and the KVM cpu id don't match.

So let's start with a floating interrupt test that will trigger a
floating interrupt (via SCLP) to be delivered to a CPU in the wait state.

Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Message-Id: <20211202123553.96412-3-david@redhat.com>
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>