MIPS: Octeon: Set dma_masks for octeon_mgmt device.

This allows follow-on patches to dma mapping functions to work with
the octeon mgmt device..

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
Patchwork: http://patchwork.linux-mips.org/patch/1632/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>