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

Export invalidation queue internals of each iommu device through the
debugfs.

Example of such dump on a Skylake machine:

$ sudo cat /sys/kernel/debug/iommu/intel/invalidation_queue
Invalidation queue on IOMMU: dmar1
 Base: 0x1672c9000      Head: 80        Tail: 80
Index           qw0                     qw1                     status
    0   0000000000000004        0000000000000000        0000000000000000
    1   0000000200000025        00000001672be804        0000000000000000
    2   0000000000000011        0000000000000000        0000000000000000
    3   0000000200000025        00000001672be80c        0000000000000000
    4   00000000000000d2        0000000000000000        0000000000000000
    5   0000000200000025        00000001672be814        0000000000000000
    6   0000000000000014        0000000000000000        0000000000000000
    7   0000000200000025        00000001672be81c        0000000000000000
    8   0000000000000014        0000000000000000        0000000000000000
    9   0000000200000025        00000001672be824        0000000000000000

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Link: https://lore.kernel.org/r/20200516062101.29541-14-baolu.lu@linux.intel.com


Signed-off-by: Joerg Roedel <jroedel@suse.de>