arch/nios2: add option to skip DMA sync as a part of map and unmap

arch/nios2: add option to skip DMA sync as a part of map and unmap

This change allows us to pass DMA_ATTR_SKIP_CPU_SYNC which allows us to
avoid invoking cache line invalidation if the driver will just handle it
via a sync_for_cpu or sync_for_device call.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Alexander Duyck <[email protected]>
Reviewed-by: Tobias Klauser <[email protected]>
Cc: Ley Foon Tan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>