powerpc/mpc85xx:Make L2 cache type independent of CHASSIS2

CHASSIS2 architecture never defines type of L2 cache present in SoC.
 it is dependent upon the core present in the SoC.
 for example,
    - e6500 core has L2 cluster (Kibo)
    - e5500 core has Backside L2 Cache

Signed-off-by: Prabhakar Kushwaha <prabhakar@freescale.com>