MIPS: OCTEON: Don't attempt to use nonexistent registers on OCTEON III models.

MIPS: OCTEON: Don't attempt to use nonexistent registers on OCTEON III models.

Attempts to read the nonexistent registers results in bus errors.
Either use registers that exist, or don't do the access as appropriate.

Signed-off-by: David Daney <david.daney@cavium.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/12502/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>