The ppc_md->init() function is currently only present on 32 bit,
if we decide that this is the way to go, we should make it common
to both 32 and 64 bit platforms.

I still think we should do something like platform_xxx_initcall(); with
xxx being {core,subsys,device,...} ... I'll look into it. ppc_md.init()
is a bit gross.

Ben.