[Patch] Add name_to_handle_at and open_by_handle_at for PowerPC

[Roland McGrath]

> Should this cleanup also take care of the ports/ implementations?

The nature of the cleanup I described is that after the new file goes in,
it would be up to each architecture independently to start using it to
reduce their duplication.

> In theory, I'd expect the vast majority of that new file to be sharable 
> across the architectures.

The sole point of the new file would be to contain exactly that which is
sharable across all architectures.