MIPS: Select CONFIG_HANDLE_DOMAIN_IRQ and make it work.

Per the subject, always select HANDLE_DOMAIN_IRQ, and implement
set_irq_regs() so that it actually works.

Signed-off-by: David Daney <david.daney@cavium.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/12496/


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