Pull more dma-mapping updates from Christoph Hellwig:

 - various swiotlb cleanups

 - do not dip into the ѕwiotlb pool for dma coherent allocations

 - add support for not cache coherent DMA to swiotlb

 - switch ARM64 to use the generic swiotlb_dma_ops

* tag 'dma-mapping-4.20-1' of git://git.infradead.org/users/hch/dma-mapping:
  arm64: use the generic swiotlb_dma_ops
  swiotlb: add support for non-coherent DMA
  swiotlb: don't dip into swiotlb pool for coherent allocations
  swiotlb: refactor swiotlb_map_page
  swiotlb: use swiotlb_map_page in swiotlb_map_sg_attrs
  swiotlb: merge swiotlb_unmap_page and unmap_single
  swiotlb: remove the overflow buffer
  swiotlb: do not panic on mapping failures
  swiotlb: mark is_swiotlb_buffer static
  swiotlb: remove a pointless comment