common: DMA-mapping: add NON-CONSISTENT attribute

DMA_ATTR_NON_CONSISTENT lets the platform to choose to return either
consistent or non-consistent memory as it sees fit.  By using this API,
you are guaranteeing to the platform that you have all the correct and
necessary sync points for this memory in the driver.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>