MIPS: ralink: add CPU interrupt controller to of_irq_ids

Convert the ralink IRQ code to make use of the new MIPS IRQ controller OF
mappings.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Signed-off-by: John Crispin <blogic@openwrt.org>
Acked-by: David Daney <david.daney@cavium.com>
Patchwork: http://patchwork.linux-mips.org/patch/4900/