MIPS: Allow forced irq threading

All low level interrupts have been marked NO_THREAD, so MIPS can enjoy
the wonderful world of forced threaded interrupt handlers.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
To: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/2639/


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