iommu/iommu-debug: Add translation and mapping test files

Running ATOS commands on custom mappings is a useful tool for debugging.
Add a new debugfs file for interactively attaching, detaching, mapping,
unmapping, and issuing ATOS commands.

Example usage:

    # cd /sys/kernel/debug/iommu/tests/soc:qcom,msm-audio-ion
    # echo 1 > attach
    # echo 0x1000,0x5000,0x1000,1 > map
    # echo 0x1008 > atos
    # cat atos
    0x5008
    # echo 0x2000 > atos
    # cat atos
    FAIL
    # echo 0 > attach

Change-Id: I596cd3f05fcb59653e2acddc17d175855a1eb9a1
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>