Diagnosis from Christian Vogel <vogel@skunk.physik.uni-erlangen.de>

cpu_idle() tests pm_idle() just once then falls into the

	while (!need_resched())
		idle();

loop.

Problem is, that loop never terminates (need_resched() always returns false
on preemptive kernels).

The other problem is that ACPI updates pm_idle _after_ cpu_idle() has taken a
local copy.  So we always call default_idle(), even when pm_idle is pointing
at a new idle handler.

So fix it to pick up changed values of pm_idle() each time around the inner
loop.