Mac/m68k Nubus updates
  - Use nubus_{read,write}[bwl]()
  - Fix /proc/bus/nubus
  - Fix type and linkage of nubus_init()
  - Use nubus_{read,write}[bwl]()
  - Kill some address assignment warnings
  - Include <asm/nubus.h>
  - nubus_init() is an initcall, hence static