iommu/iommu-debug: Use more iterations while profiling

Currently we only take one sample per buffer size per API when doing
profiling.  This results in high run-to-run variance in the results.
Use more iterations to help smooth this out.

Change-Id: I3779007a2f69ef79b573285b2422554f42dda99f
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>