[POWERPC] 85xx: Add device nodes for error reporting devices used by EDAC

Adding memory-controller and l2-cache-controller entries to be used by EDAC
as of_devices for MPC8541 CDS, MPC8544 DS, MPC8555 CDS, and MPC8568 MDS.

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