[POWERPC] 85xx: Add next-level-cache property

Added next-level-cache to the L1 and a reference to the new L2 label.
This is per the ePAPR 0.94 spec.  Since we are't really dependent on this
today we aren't supporting the "legacy" l2-cache phandle that is specified
in the PPC v2.1 OF Binding spec.

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