Add support for cpu notification chain. This is useful with nested virtualization when Xen runs as l1 hypervisor. This cleans up mce initialization cleanup as a side-effect. Signed-off-by: Christoph Egger -- ---to satisfy European Law for business letters: Advanced Micro Devices GmbH Einsteinring 24, 85689 Dornach b. Muenchen Geschaeftsfuehrer: Alberto Bozzo Sitz: Dornach, Gemeinde Aschheim, Landkreis Muenchen Registergericht Muenchen, HRB Nr. 43632