run acpi_shutdown_final later to give other handlers a chance

For example, shutdown_panic wants to produce some output and maybe take
some input before a system is actually reset.

The change should only make difference for the case of system reset
(reboot), poweroff and halt should not be affected.

The change makes difference only if hw.acpi.handle_reboot is set. It
used to default to zero until r213755 / ac731af5670c7.