Add mcelog support from xen platform

Add mcelog support from xen platform

This patch backport from Jeremy's pvops commit a5ed1f3dae179158e385e9371462dd65d5e125c5,
which in turn backport from previous xen DOM0(2.6.18) cs: 75e5bfa7fbdc

When a MCE/CMCI error happens (or by polling), the related error
information will be sent to privileged pv-ops domain by XEN. This
patch will help to fetch the xen-logged information by hypercall
and then convert XEN-format log into Linux format MCELOG. It makes
using current available mcelog tools for native Linux possible.

With this patch, after mce/cmci error log information is sent to
pv-ops guest, Running mcelog tools in the guest, you will get same
detailed decoded mce information as in Native Linux.

Signed-off-by: Liu, Jinsong <jinsong.liu@intel.com>
Signed-off-by: Ke, Liping <liping.ke@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>