Commit b5c58b2f ("dma-mapping: direct calls for dma-iommu") switched
to use direct calls to dma-iommu, but missed the dma_vmap_noncontiguous,
dma_vunmap_noncontiguous and dma_mmap_noncontiguous behavior keyed off the
presence of the alloc_noncontiguous method.

Fix this by removing the now unused alloc_noncontiguous and
free_noncontiguous methods and moving the vmapping and mmaping of the
noncontiguous allocations into the iommu code, as it is the only provider
of actually noncontiguous allocations.

Fixes: b5c58b2f ("dma-mapping: direct calls for dma-iommu")
Reported-by: Xi Ruoyao <xry111@xry111.site>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Leon Romanovsky <leon@kernel.org>
Tested-by: Xi Ruoyao <xry111@xry111.site>