swiotlb: Use dma_direct_supported() for swiotlb_ops

swiotlb_alloc() calls dma_direct_alloc(), which can satisfy lower than 32-bit
DMA mask requests using GFP_DMA if the architecture supports it. Various
x86 drivers rely on that, so we need to support that. At the same time
the whole kernel expects a 32-bit DMA mask to just work, so the other magic
in swiotlb_dma_supported() isn't actually needed either.

Reported-by: Dominik Brodowski <[e-mail]>
Signed-off-by: Christoph Hellwig <[e-mail]>
Cc: Konrad Rzeszutek Wilk <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: [e-mail]
Fixes: 6e4bf5867783 ("x86/dma: Use generic swiotlb_ops")
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

lib/swiotlb.c

···
 	.unmap_sg		= swiotlb_unmap_sg_attrs,
 	.map_page		= swiotlb_map_page,
 	.unmap_page		= swiotlb_unmap_page,
-	.dma_supported		= swiotlb_dma_supported,
+	.dma_supported		= dma_direct_supported,
 };
 #endif /* CONFIG_DMA_DIRECT_OPS */