iommu: iommu-debug: cleanup iommu debug

Only expose debugfs nodes for test devices.
Restrict secure attach to a valid vmid.
Add clock reference counting to make code more robust.
Restrict address printing with kptr_restrict.

Change-Id: Ibf90068d778b0156e3bb42287af5dda3864da5fc
Signed-off-by: Liam Mark <lmark@codeaurora.org>