MIPS: OCTEON: Add model checking support for cn73xx, cnf75xx and cn78xx

Follow on patchs need to be able to distinguish the new models.

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/12498/


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