treewide: Consolidate get_dma_ops() implementations

treewide: Consolidate get_dma_ops() implementations

Introduce a new architecture-specific get_arch_dma_ops() function
that takes a struct bus_type * argument. Add get_dma_ops() in
<linux/dma-mapping.h>.

Signed-off-by: Bart Van Assche <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Boris Ostrovsky <[email protected]>
Cc: David Woodhouse <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: Russell King <[email protected]>
Cc: [email protected]
Signed-off-by: Doug Ledford <[email protected]>