MIPS: Octeon: Allow access to CIU3 IRQ domains.

Add accessor function octeon_irq_get_block_domain() for cores
with a CIU3.

Signed-off-by: Steven J. Hill <steven.hill@cavium.com>
Acked-by: David Daney <david.daney@cavium.com>
Cc: linux-mips@linux-mips.org
Cc: linux-watchdog@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/17210/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>