KVM: s390: provide control registers via kvm_run

There are several cases were we need the control registers for
userspace. Lets also provide those in kvm_run.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>