MIPS: OCTEON: Supply OCTEON+ USB nodes in internal device trees.

This will be needed by the next patch to use said nodes for probing
via the device tree.

Signed-off-by: David Daney <david.daney@cavium.com>
Tested-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: John Crispin <blogic@openwrt.org>
Patchwork: http://patchwork.linux-mips.org/patch/6185/