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

Export page table internals of the domain attached to each device.
Example of such dump on a Skylake machine:

$ sudo cat /sys/kernel/debug/iommu/intel/domain_translation_struct
[ ... ]
Device 0000:00:14.0 with pasid 0 @0x15f3d9000
IOVA_PFN                PML5E                   PML4E
0x000000008ced0 |       0x0000000000000000      0x000000015f3da003
0x000000008ced1 |       0x0000000000000000      0x000000015f3da003
0x000000008ced2 |       0x0000000000000000      0x000000015f3da003
0x000000008ced3 |       0x0000000000000000      0x000000015f3da003
0x000000008ced4 |       0x0000000000000000      0x000000015f3da003
0x000000008ced5 |       0x0000000000000000      0x000000015f3da003
0x000000008ced6 |       0x0000000000000000      0x000000015f3da003
0x000000008ced7 |       0x0000000000000000      0x000000015f3da003
0x000000008ced8 |       0x0000000000000000      0x000000015f3da003
0x000000008ced9 |       0x0000000000000000      0x000000015f3da003

PDPE                    PDE                     PTE
0x000000015f3db003      0x000000015f3dc003      0x000000008ced0003
0x000000015f3db003      0x000000015f3dc003      0x000000008ced1003
0x000000015f3db003      0x000000015f3dc003      0x000000008ced2003
0x000000015f3db003      0x000000015f3dc003      0x000000008ced3003
0x000000015f3db003      0x000000015f3dc003      0x000000008ced4003
0x000000015f3db003      0x000000015f3dc003      0x000000008ced5003
0x000000015f3db003      0x000000015f3dc003      0x000000008ced6003
0x000000015f3db003      0x000000015f3dc003      0x000000008ced7003
0x000000015f3db003      0x000000015f3dc003      0x000000008ced8003
0x000000015f3db003      0x000000015f3dc003      0x000000008ced9003
[ ... ]

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>