MIPS: BCM63xx: Allow setting affinity for IPIC

Wire up the set_affinity call for the internal PIC if booting on
a cpu supporting it.
Affinity is kept to boot cpu as default.

Signed-off-by: Jonas Gorski <jogo@openwrt.org>
Cc: linux-mips@linux-mips.org
Cc: John Crispin <blogic@openwrt.org>
Cc: Maxime Bizon <mbizon@freebox.fr>
Cc: Florian Fainelli <florian@openwrt.org>
Cc: Kevin Cernekee <cernekee@gmail.com>
Cc: Gregory Fong <gregory.0xf0@gmail.com>
Patchwork: https://patchwork.linux-mips.org/patch/7323/


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