Master and powerpc-next branches reset

Due to the "Free a PTE bit on ppc64 with 64K pages" commit from Ben H
turning out to be bad, I have reset the master and powerpc-next
branches of the powerpc.git repository to the commit just before that,
and then reapplied the "powerpc: Remove arch/ppc and include/asm-ppc"
commit (taking the opportunity to add John Linn's acked-by).

So if you pull either or both of those branches, you'll need to do a
git pull -f next time.  I prefer not to reset branches if possible,
but it seemed necessary to remove the bad commit in this case so as
not to cause bisection problems later.

Paul.