s390x: copy sclp.h and sclp-ascii.c from QEMU

The s390x-ccw pcbios already has what we need to print to the sclp
console. Let's copy the files and adjust them to our needs later.

Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20170522085702.17856-4-david@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>