Hypercall to expose physical CPU information.

Hypercall to expose physical CPU information.

It also make some changes to current cpu online/offline logic:
1) Firstly, cpu online/offline will trigger a vIRQ to dom0 for status
changes notification.
2) It also add an interface to platform operation to online/offline
physical CPU. Currently the cpu online/offline interface is in sysctl,
which can't be triggered in kernel. With this change, it is possible
to trigger cpu online/offline in dom0 through sysfs interface.

Signed-off-by: Jiang, Yunhong <yunhong.jiang@intel.com>