ARM64: dma-mapping: get gap/prefetch from mapping

ARM64: dma-mapping: get gap/prefetch from mapping

if prefetch or gap are specified from mapping, then
use mapping's properties. Else, assume that this
mapping is still not updated and fall back to using
DMA_ATTR_SKIP_IOVA_GAP attribute.

Bug 1463797

Change-Id: I4cef73adc5ffbb43389f7d31f6684d82f9fefa16
Signed-off-by: Sri Krishna chowdary <schowdary@nvidia.com>
Reviewed-on: http://git-master/r/413269
GVS: Gerrit_Virtual_Submit
Reviewed-by: Hiroshi Doyu <hdoyu@nvidia.com>
Tested-by: Hiroshi Doyu <hdoyu@nvidia.com>