x86: blacklist new AMD CPUID bits for PV domains

x86: blacklist new AMD CPUID bits for PV domains

there are some new CPUID bits (and leaves) which Dom0 and PV domains
should not see to avoid trouble, since we don't emulate the features.
The most prominent one is a topology leaf, which contains information
specific to the physical CPU, not the virtual one. To avoid confusion
(and possibly crashes) due to a confused Dom0 scheduler simply disable
these bits.

Signed-off-by: Andre Przywara <andre.przywara@amd.com>
Signed-off-by: Keir Fraser <keir@xen.org>