iommu/iommu-debug: Make attachment directories unique

Currently, the device name for the SMMU context bank device is used as
the filename for the IOMMU debug info file.  This doesn't work in cases
where multiple domains can be attached to a single SMMU context bank
device (like dynamic domains).  Make these filenames unique by appending
a 16-byte uuid to the name.

Change-Id: Ie26ece773bfa2e8c75a329a8cb8461bcd598218e
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>