Starting the arch/powerpc merge

I have pushed a commit to the powerpc-merge.git tree which gets us far
enough to be able to build a 32-bit powermac kernel with
ARCH=powerpc.  It's still very rough in places, and it uses bits out
of arch/ppc/kernel and arch/ppc/syslib, but it is a start.

Of course, this means that we are about to bump up against the really
hard bits of the merge.  Things like

* converting ppc32 to use the lmb infrastructure
* introducing the device-tree flattening/unflattening to ppc32
* working out how to deal with the early hash table initialization
  that POWER4 needs on ppc32
* reconciling the fact that ppc64 needs RELOC in the prom_init code,
  whereas ppc32 doesn't; but ppc64 doesn't need RELOC when running
  with the MMU off but ppc32 does (or needs -mrelocatable).

I look forward to people sending me patches to push this on a bit
further, and in particular to populate arch/powerpc/platforms a bit
more. :)

Paul.