iommu/iommu-debug: Add file for profiling the fast DMA APIs

The fast DMA API implementation that was recently needs to be profiled.
Add a new debugfs file (similar to the original "profiling" file) to do
this.

CRs-Fixed: 997751
Change-Id: I1236d9b6aaeab9d34b39e7f5d7b285691d1779da
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>