MIPS: Hook Cavium OCTEON cache init into cache.c

Follow precedent of other boards, and hook-up the CPU specific cache
init.

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>