dma-mapping: consolidate the dma mmap implementations

The only functional differences (modulo a few missing fixes in the arch
code) is that architectures without coherent caches need a hook to
convert a virtual or dma address into a pfn, given that we don't have
the kernel linear mapping available for the otherwise easy virt_to_page
call.  As a side effect we can support mmap of the per-device coherent
area even on architectures not providing the callback, and we make
previous dangerous default methods dma_common_mmap actually save for
non-coherent architectures by rejecting it without the right helper.

In addition to that we need a hook so that some architectures can
override the protection bits when mmaping a dma coherent allocations.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Paul Burton <paul.burton@mips.com> # MIPS parts

drivers/xen/swiotlb-xen.c

@@ -662,7 +662,7 @@ xen_swiotlb_dma_mmap(struct device *dev, struct vm_area_struct *vma,
 		return xen_get_dma_ops(dev)->mmap(dev, vma, cpu_addr,
 						    dma_addr, size, attrs);
 #endif
-	return dma_common_mmap(dev, vma, cpu_addr, dma_addr, size);
+	return dma_common_mmap(dev, vma, cpu_addr, dma_addr, size, attrs);
 }
 
 /*