iommu: msm: add barrier call on coherent lazy map

When clients of the lazy APIs enable IO coherency they will
skip their cache maintenance code.
However before passing a coherent buffer to the device for
DMA a barrier call must still be made to ensure the caches
are up to date.

Add this barrier call to the lazy map function when
IO coherency is enabled.

Change-Id: I3fc065f8aeff705283211e59bd641d81b4e74067
Signed-off-by: Liam Mark <lmark@codeaurora.org>