Register for the extended sleep callback from ACPI.

As tboot currently does not support the reduced hardware sleep
interface, fail this extended sleep call.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Ben Guthro <benjamin.guthro@citrix.com>
Cc: tboot-devel@lists.sourceforge.net
Cc: Gang Wei <gang.wei@intel.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>