MIPS: Netlogic: PIC IRQ handling update for multi-chip

Create struct nlm_pic_irq for interrupts handled by the PIC.
This simplifies IRQ handling for multi-SoC as well as
the single SoC cases. Also split the setup of percpu and PIC
interrupts so that we can configure the PIC interrupts for
every node.

Signed-off-by: Jayachandran C <jchandra@broadcom.com>
Patchwork: http://patchwork.linux-mips.org/patch/4467
Signed-off-by: John Crispin <blogic@openwrt.org>