MIPS: ralink: add illegal access driver

These SoCs have a special irq that fires upon an illegal memmory access.

Signed-off-by: John Crispin <blogic@openwrt.org>
Patchwork: http://patchwork.linux-mips.org/patch/8003/


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