dma: add dma_*map*_attrs() interfaces

Introduce new interfaces, dma_*map*_attrs(), for passing architecture-specific
attributes when memory is mapped and unmapped for DMA.  Give the interfaces
default implementations which ignore attributes.  Also introduce the
dma_{set|get}_attr() interfaces for setting and retrieving individual
attributes.  Define one attribute, DMA_ATTR_WRITE_BARRIER, in anticipation of
its use by ia64/sn.  Select whether architectures implement arch-specific
versions of the dma_*map*_attrs() interfaces via HAVE_DMA_ATTRS in Kconfig.

[[email protected]: dma_{set,get}_attr() have to be static inline]
Signed-off-by: Arthur Kepner <[email protected]>
Cc: Tony Luck <[email protected]>
Cc: Jesse Barnes <[email protected]>
Cc: Jes Sorensen <[email protected]>
Cc: Randy Dunlap <[email protected]>
Cc: Roland Dreier <[email protected]>
Cc: James Bottomley <[email protected]>
Cc: David Miller <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Grant Grundler <[email protected]>
Cc: Michael Ellerman <[email protected]>
Signed-off-by: Mark Nelson <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

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