powerpc: wii: hollywood interrupt controller support

Add support for the dual interrupt controller included in the "Hollywood"
chipset of the Nintendo Wii video game console.
This interrupt controller serves both the Broadway processor (as a cascade)
and the Starlet processor, and is used to manage interrupts for the
non-classic hardware.

Signed-off-by: Albert Herranz <albert_herranz@yahoo.es>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Segher Boessenkool <segher@kernel.crashing.org>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>