x86: cpuid faulting feature enable

x86: cpuid faulting feature enable

Latest Intel processor add cpuid faulting feature. This patch is used
to support cpuid faulting in Xen.  Like cpuid spoofing, cpuid faulting
mainly used to support live migration. When cpuid faulting enabled,
cpuid instruction runs at cpl>0 will produce GP, vmm then emulate
execution of the cpuid instruction. Hence will appear to guest
software the value chosen by the vmm.

Signed-off-by: Liu, Jinsong <jinsong.liu@intel.com>
Signed-off-by: Keir Fraser <keir@xen.org>