x86: New vcpu_op call to get physical CPU identity.

x86: New vcpu_op call to get physical CPU identity.

Some AMD machines have APIC IDs that not equal to CPU IDs. In
the default Xen configuration, ACPI calls on these machines
can get confused. This shows up most noticeably when running
AMD PowerNow!. The only solution is for dom0 to get the
hypervisor's cpuid to apicid table when needed (ie, when dom0
vcpus are pinned).

Add a vcpu op to Xen to allow dom0 to query the hypervisor for
architecture dependent physical cpu information if dom0 vcpus are
pinned.

Signed-off-by: Mark Langsdorf <mark.langsdorf@amd.com>
Signed-off-by: Keir Fraser <keir.fraser@citrix.com>