dma-iommu: Ensure iova is within given range

Ensure iova is within range specified in iommu_dma_init_domain().
This also prevents unnecessary work iterating through the entire
rb_tree.

Change-Id: I3f3580e9c54db06d22d5456dabdc2cec6fee07bc
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>