libx86: Share struct cpuid_policy with userspace

libx86: Share struct cpuid_policy with userspace

Both Xen and the toolstack have need of the same logic when it comes to
manipulation and checking of the CPUID and MSR values offered to guests.  To
that end, libx86 is being introduced to allow Xen and the toolstack to share a
single implementation, rather than duplicating the logic.

No functional change.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>