Otherwise tight loops at smt_low for example, which OPAL does,
eat so much CPU that we can't boot a kernel anymore. With that,
I can boot 8 CPUs just fine with powernv.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>