[POWERPC] cell: Add Cell memory controller register defs and expose it

This adds definitions for the Cell memory controller registers (at
least some of them) for use by the EDAC driver for ECC error reporting.

It also expose the said MIC as a platform device that can be used
by the EDAC driver to match on.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>