x86 / tboot / ACPI: Fail extended mode reduced hardware sleep

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>