[POWERPC][v2] Bolt in SLB entry for kernel stack on secondary cpus

[Paul Mackerras]

David Gibson writes:

> Do you even need the processor ID test at all?  The boot processor
> should always have its stack covered by SLB entry 0 when we come
> through here, shouldn't it?

I was concerned that get_paca()->kstack wouldn't have been initialized
by the time the boot cpu calls slb_initialize().  If that fear is
unfounded then the check could go.

Paul.