[POWERPC] Add DMA ops support for of_platform_device to Cell

This patch adds a bus device notifier to the of_platform bus type on
cell to setup the DMA operations for of_platform_devices. We currently
use the PCI operations as Cell use a special version of them that
happens to be suitable for our needs.

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