[POWERPC] 4xx: remove bogus "ranges" property in Bamboo EBC node

This removes a bogus empty "ranges" property in the EBC device node
of the Bamboo board device-tree.

The "ranges" property should be created by the wrapper code when it is
implemented.  Until then, remove the empty property since it incorrectly
implies that there is a 1:1 address mapping between the EBC and the OPB.

This also fixes a warning from newer DTCs.

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