MIPS: Octeon: Put restrictions on DMA descriptors.

Set the DMA mask such that all descriptors stay in the
lower 4GB of memory.

Signed-off-by: Steven J. Hill <steven.hill@cavium.com>
Acked-by: David Daney <david.daney@cavium.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/13830/


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