ppc/85xx/86xx: Device tree fixup for number of cores

Fixing the number of cores in the device tree based on the actual number of
cores on the system.  With this same device tree image can be used for dual
core and single core members of otherwise exactly same SOC.

For example:
* P2020RDB and P2010RDB
* P1020RDB and P1011RDB
* MPC8641D and MPC8641

Signed-off-by: Poonam Aggrwal <poonam.aggrwal@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>