[CELL] driver for DDR2 memory on AXON

The Axon bridge chip used on new Cell/B.E. based blade servers
comes with a DDR2 memory controller that can be used to
attach cheap memory modules, as opposed to the high-speed
XDR memory that is used by the CPU itself.

Since the memory controller does not participate in the
cache coherency protocol, we can not use the memory direcly
for Linux applications, but by providing a block device
it can be used for swap space, temporary file storage and
through the use of the direct_access block device operation
for mapping into user addresses, when it is mounted with
an appropriate file system.

Signed-off-by: Maxim Shchetynin <maxim@de.ibm.com>
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>