* make PowerPC NVRAM accessors generic to be able to use a MacIO NVRAM
  instead of the M48T59 one
* split PowerMac targets code:
 - move all PowerMac related definitions and prototypes into hw/ppc_mac.h
 - add hw/mac_dbdma.c, hw/mac_nvram.c and macio.c
   which implements shared PowerMac devices
 - define the g3bw machine in a new hw/ppc_oldworld.c file
* Fix the g3bw target:
 - fix the Grackle host PCI device
 - connect the Heathrow PIC to the PowerPC 6xx bus pins


git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@3475 c046a42c-6fe2-441c-8c8c-71466251a162