MIPS: Octeon: Setup irq_domains for interrupts.

Create two domains.  One for the GPIO lines, and the other for on-chip
sources.

Signed-off-by: David Daney <david.daney@cavium.com>
Cc: linux-mips@linux-mips.org
Cc: devicetree-discuss@lists.ozlabs.org
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: linux-kernel@vger.kernel.org
Cc: David Daney <david.daney@cavium.com>
Patchwork: https://patchwork.linux-mips.org/patch/3936/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>