iommu/vt-d: Add debugfs support to show context internals

Export Intel IOMMU DMA remapping internal states, such as root and
context table entries in debugfs.

Example of such dump in Kabylake:
/sys/kernel/debug/iommu/intel/dmar_translation_struct

IOMMU dmar0: Root Table Address:45699c000
Root Table Entries:
 Bus: 0 H: 0 L: 45699f001
 Context Table Entries for Bus: 0
  Entry B:D.F   High    Low
  16    00:02.0 102     45699e005

IOMMU dmar1: Root Table Address:45699d000
Root Table Entries:
 Bus: 0 H: 0 L: 45644f001
 Context Table Entries for Bus: 0
  Entry B:D.F   High    Low
  160   00:14.0 102     45644e001
  184   00:17.0 302     456310001
  248   00:1f.0 202     4564bf001

Cc: Lu Baolu <baolu.lu@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Ashok Raj <ashok.raj@intel.com>
Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
Co-Developed-by: Gayatri Kammela <gayatri.kammela@intel.com>
Signed-off-by: Gayatri Kammela <gayatri.kammela@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Sohil Mehta <sohil.mehta@intel.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>