remove dead powernv code v2

[Christoph Hellwig]

ping?

On Thu, May 23, 2019 at 09:49:20AM +0200, Christoph Hellwig wrote:
> Hi all,
> 
> the powerpc powernv port has a fairly large chunk of code that never
> had any upstream user.  We generally strive to not keep dead code
> around, and this was affirmed at least years Maintainer summit.
> 
> Changes since v1:
>  - rebased to v5.2-rc1
>  - remove even more dead code
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