s390x: add a test case for the ipm + spm instructions

Add a new file "emulator.c" and keep running tests simple for now
(no support for multiple iterations and such stuff). We will get this
for free once we switch to a new, general API for running/defining
tests.

Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20170919145033.16959-2-david@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>