Currently it's hard to get CPU's microcode revision from Xen after late
loading without looking into Xen logs, which is not always convenient.
Add a new platform op in order to get the required data from Xen and
provide a wrapper for libxenctrl.
Signed-off-by: Sergey Dyasli <sergey.dyasli@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>