irqdomain: Remove temporary MIPS workaround code

The MIPS interrupt controllers are all registering their own irq_domains
now. Drop the MIPS specific code because it is no longer needed.

Signed-off-by: Grant Likely <grant.likely@linaro.org>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/5458/


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