Connect macppc's power button and lid to the SUSPEND stubs

Connect macppc's power button and lid to the SUSPEND stubs

A kernel with option SUSPEND now calls gosleep() if I run zzz(8),
press the power button (when machdep.pwraction=2), or close the lid
(when machdep.lidaction=1).  Because gosleep() is an empty stub, the
macppc does not really suspend; it only suspends some devices and
immediately resumes.

The interrupt from the power button or the lid needs some thread
(other than systq) to call sleep_state().  Use taskq_create(9) to
create another thread.

Add a call to device_register_wakeup().  Without this call,
sleep_state() does nothing.

ok kettenis@ deraadt@