arm64: use asm-generic/dma-mapping.h

Now that the Xen special cases are gone nothing worth mentioning is
left in the arm64 <asm/dma-mapping.h> file, so switch to use the
asm-generic version instead.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Will Deacon <will@kernel.org>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

arch/arm64/mm/dma-mapping.c

@@ -8,6 +8,7 @@
 #include <linux/cache.h>
 #include <linux/dma-noncoherent.h>
 #include <linux/dma-iommu.h>
+#include <xen/xen.h>
 #include <xen/swiotlb-xen.h>
 
 #include <asm/cacheflush.h>