Xen: Export host physical CPU information to dom0

Xen: Export host physical CPU information to dom0

This patch rebased from Jeremy's pvops commit
3b34cd19627c6e191b15fd6cb59f997b8db21e19 and
68320323a51c2378aca433c76157d9e66104ff1e

This patch expose host's physical CPU information to dom0 in sysfs, so
that dom0's management tools can control the physical CPU if needed.

It also provides interface in sysfs to logical online/offline a physical CPU.

Notice: The information in dom0 is synced with xen hypervisor asynchronously.

Signed-off-by: Liu, Jinsong <jinsong.liu@intel.com>
Signed-off-by: Jiang, Yunhong <yunhong.jiang@intel.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>