MIPS: Octeon: Implement Octeon specific __copy_user_inatomic

The generic version seems to prefetch past the end of memory.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/3929/


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