MIPS: Octeon: Replace rwlocks in irq_chip handlers with raw_spinlocks.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
Cc: linux-mips@linux-mips.org
Patchwork: http://patchwork.linux-mips.org/patch/972/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>