[Intel-gfx] susetting the remaining swioltb couplin in DRM

[Christoph Hellwig]

Hi i915 and nouveau maintainers,

any chance I could get some help to remove the remaining direct
driver calls into swiotlb, namely swiotlb_max_segment and
is_swiotlb_active.  Either should not matter to a driver as they
should be written to the DMA API.

In the i915 case it seems like the driver should use
dma_alloc_noncontiguous and/or dma_alloc_noncoherent to allocate
DMAable memory instead of using alloc_page and the streaming
dma mapping helpers.

For the latter it seems like it should just stop passing
use_dma_alloc == true to ttm_device_init and/or that function
should switch to use dma_alloc_noncoherent.