KVM: s390 features, kvm_get_vcpu_by_id and stat
Several features for s390
1. ESCA support (up to 248 vCPUs)
2. KVM detection: we can now detect if we support KVM (e.g. does KVM
under KVM work?)
kvm_stat:
1. cleanup the exit path
kvm_get_vcpu_by_id:
1. Use kvm_get_vcpu_by_id where appropriate
2. Apply a heuristic to optimize for ID VCPU == No. VCPU