85xx: Add support for e500mc cache stashing

The e500mc core supports the ability to stash into the L1 or L2 cache,
however we need to uniquely identify the caches with an id.

We use the following equation to set the various stash-ids:

32 + coreID*2 + 0(L1) or 1(L2)

The 0 (for L1) or 1 (for L2) matches the CT field used be various cache
control instructions.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>