iommu: Update the offset of the extended domain attributes

There is a slim possibility that the domain attribute values
might overlap if one was using an older module against a newer
kernel. Avoid the possibility of conflict by offsetting the
atttributes by 16 and then fix up the arm-smmu driver so that
we can still use the attributes as bit positions in a u64
bitmask.

Change-Id: Ic0dedbad867af1c99e18793d1136ac677b0e73d9
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>