powerpc/mpc8xxx: fix core id for multicore booting

For the cores with multiple threads, we need to figure out which physical
core a thread belongs. To match the core ids, update PIR registers and
spin tables.

Signed-off-by: York Sun <yorksun@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Andy Fleming <afleming@freescale.com>