powerpc/mpc85xx: Enable L2 at the beginning of U-boot for E6500

Using E6500 L1 cache as initram requires L2 cache enabled.
Add l2-cache cluster enabling.

Setup stash id for L1 cache as (coreID) * 2 + 32 + 0
Setup stash id for L2 cache as (cluster) * 2 + 32 + 1
Stash id for L2 is only set for Chassis 2.

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>