powerpc: wii: allow ioremap within the memory hole

Enable the flag that allows a platform to ioremap memory marked
as reserved.

This is currently needed on the Nintendo Wii video game console
due to the workaround introduced in "wii: use both mem1 and mem2 as ram".

This will no longer be needed when proper discontig memory support
for 32-bit PowerPC is added to the kernel.

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