Currently we do a spin on secondary cpus when waiting to boot. This
theoretically causes issues with power consumption and does cause issues
with qemu cycle burning (it starves cpu 0 from actually being able to
boot.)
This change puts each secondary cpu to sleep if they have a power
management unit, then signals them to wake via IPI when its time to boot.
If the cpus have no power management unit they will loop as before.
Note: The wakeup IPI requires a special interrupt handler as on secondary
cpu's the interrupt infrastructure is not yet established. This
interrupt handler is set and reset by updating SPR_EVBAR.
Signed-off-by: Stafford Horne <shorne@gmail.com>
c056718464