cleanup swiotlb initialization

[Christoph Hellwig]

On Thu, Feb 24, 2022 at 11:18:33AM -0500, Boris Ostrovsky wrote:
>
> On 2/24/22 10:58 AM, Christoph Hellwig wrote:
>> Thanks.
>>
>> This looks really strange as early_amd_iommu_init should not interact much
>> with the changes.  I'll see if I can find a AMD system to test on.
>
>
> Just to be clear: this crashes only as dom0. Boots fine as baremetal.

Ah.  I can gues what this might be.  On Xen the hypervisor controls the
IOMMU and we should never end up initializing it in Linux, right?