MIPS: Add Cavium OCTEON processor constants and CPU probe.

Add OCTEON constants to asm/cpu.h and asm/module.h.

Add probe function for Cavium OCTEON CPUs and hook it up.

Signed-off-by: Tomaso Paoletti <tpaoletti@caviumnetworks.com>
Signed-off-by: David Daney <ddaney@caviumnetworks.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>