iommu/iommu-debug: Only uniquify directory names for dynamic domains

The subdirectories under "attach" currently get a UUID appended to their
name to ensure that there won't be any collisions when multiple domains
are attached to the same device.  This is only needed for dynamic
domains since those are the only types of domains that can be attached
to the same device concurrently.  Only do the uniquification for dynamic
domains since the resulting directory name is a bit messy with the UUID.

Change-Id: Ia86b192e5b9d6a63132228fa86549a2977ec74a4
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>