s390x/kvm: Handle bpb feature

s390x/kvm: Handle bpb feature

We need to handle the bpb control on reset and migration. Normally
stfle.82 is transparent (and the normal guest part works without
hypervisor activity). To prevent any issues we require full
host kernel support for this feature.

Cc: [email protected]
Signed-off-by: Christian Borntraeger <[email protected]>
Message-Id: <20180118085628[email protected]>
Reviewed-by: Thomas Huth <[email protected]>
Reviewed-by: David Hildenbrand <[email protected]>
[CH: 'Branch Prediction Blocking' -> 'Branch prediction blocking']
Signed-off-by: Cornelia Huck <[email protected]>