KVM: s390: protvirt: Add UV cpu reset calls

For protected VMs, the VCPU resets are done by the Ultravisor, as KVM
has no access to the VCPU registers.

Note that the ultravisor will only accept a call for the exact reset
that has been requested.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
[borntraeger@de.ibm.com: patch merging, splitting, fixing]
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>