With win8 capabiltiy, the machine will boot itself immediately after
shutdown command has executed.

Work around this issue by disabling win8 capcability.  This workaround
also makes wireless hotkey work.
Signed-off-by: Edward Lin <yidi.lin@canonical.com>
Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>