use generic dma-direct and swiotlb code for x86

[Christoph Hellwig]

Hi all,

this series switches the x86 code the the dma-direct implementation
for direct (non-iommu) dma and the generic swiotlb ops.  This includes
getting rid of the special ops for the AMD memory encryption case and
the STA2x11 SOC.  The generic implementations are based on the x86
code, so they provide the same functionality.