iommu/vt-d: Add debugfs support to show scalable mode DMAR table internals

A DMAR table walk would typically follow the below process.
1. Bus number is used to index into root table which points to a context
   table.
2. Device number and Function number are used together to index into
   context table which then points to a pasid directory.
3. PASID[19:6] is used to index into PASID directory which points to a
   PASID table.
4. PASID[5:0] is used to index into PASID table which points to all levels
   of page tables.

Whenever a user opens the file
"/sys/kernel/debug/iommu/intel/dmar_translation_struct", the above
described DMAR table walk is performed and the contents of the table are
dumped into the file. The dump could be handy while dealing with devices
that use PASID.

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

(Please note that because of 80 char limit, entries that should have been
in the same line are broken into different lines)

IOMMU dmar0: Root Table Address: 0x436f7c000
B.D.F	Root_entry				Context_entry
PASID	PASID_table_entry
00:0a.0	0x0000000000000000:0x000000044dd3f001	0x0000000000100000:0x0000000435460e1d
0	0x000000044d6e1089:0x0000000000000003:0x0000000000000001
00:0a.0	0x0000000000000000:0x000000044dd3f001	0x0000000000100000:0x0000000435460e1d
1	0x0000000000000049:0x0000000000000001:0x0000000003c0e001

Note that the above format is followed even for legacy DMAR table dump
which doesn't support PASID and hence in such cases PASID is defaulted to
-1 indicating that PASID and it's related fields are invalid.

Cc: Joerg Roedel <joro@8bytes.org>
Cc: Ashok Raj <ashok.raj@intel.com>
Cc: Lu Baolu <baolu.lu@linux.intel.com>
Cc: Sohil Mehta <sohil.mehta@intel.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>