MIPS: Add Cavium OCTEON slot into proper tlb category.

Expand the case statement for build_tlb_write_entry so that it does
the right thing on Cavium CPU variants.

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