powerpc: wii: platform support

Add platform support for the Nintendo Wii video game console.

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>