cleanup swiotlb initialization v8

[Christoph Hellwig]

On Mon, Apr 04, 2022 at 07:05:44AM +0200, Christoph Hellwig wrote:
> Hi all,
> 
> this series tries to clean up the swiotlb initialization, including
> that of swiotlb-xen.  To get there is also removes the x86 iommu table
> infrastructure that massively obsfucates the initialization path.
> 
> Git tree:
> 
>     git://git.infradead.org/users/hch/misc.git swiotlb-init-cleanup
> 
> Gitweb:
> 
>     http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/swiotlb-init-cleanup

I've updated the git tree above with the commit message nitpicks and
received reviews.  I plan to pull the patches into the dma-mapping
tree after -rc3 is released, so if any involved maintainer is not happy
with the result, please speak up now.