MIPS: For Cavium OCTEON set hwrena and lazily restore CP2 state.

If on Cavium, be aware of cop2 and hwrena during do_cpu().

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>