[POWERPC] 4xx: Wire up 440EP USB controller support to Bamboo board

This adds the definition of the on-chip OHCI controller to the
Bamboo board's device-tree. This is enough to get it probed and
working, though a separate patch fixing a bug in the OHCI driver
is needed to make it reliable.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>