iommu: iommu-debug: Rework CONFIG_IOMMU_DEBUG_TRACKING

If CONFIG_IOMMU_DEBUG_TRACKING=y, a deadlock will occur if userspace
writes to the debugfs file "attach":

    -001|context_switch(inline)
    -001|__schedule()
    -002|__preempt_count_sub(inline)
    -002|schedule()
    -003|schedule_timeout()
    -004|do_wait_for_common(inline)
    -004|__wait_for_common(inline)
    -004|wait_for_common()
    -005|wait_for_completion()
    -006|__synchronize_srcu()
    -007|synchronize_srcu()
    -008|debugfs_remove_recursive()
    -009|iommu_debug_detach_device()
    -010|__iommu_detach_device()
    -011|__iommu_group_for_each_dev(inline)
    -011|__iommu_detach_group()
    -012|iommu_detach_device()
    -013|iommu_debug_device_profiling()
    -014|iommu_debug_device_show()
    -015|seq_read()
    -016|full_proxy_read()
    -017|__vfs_read()
    -018|vfs_read()

Since the files in the attachment directory are rarely used, remove
them. Update the data saved by this config option to work properly
with iommu groups.

Change-Id: I3f0f1d0836f37412915ce3e78d8aefe92dc8d096
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>
[lmark@codeaurora.org: deadlock is not an issue on this branch
 but this change is backported because there are security benefits
 from removing the iommu debugfs attachments nodes, such as removing
 register access.]
Signed-off-by: Liam Mark <lmark@codeaurora.org>