iommupt: Add read_and_clear_dirty op

iommupt: Add read_and_clear_dirty op

IOMMU HW now supports updating a dirty bit in an entry when a DMA writes
to the entry's VA range. iommufd has a uAPI to read and clear the dirty
bits from the tables.

This is a trivial recursive descent algorithm to read and optionally clear
the dirty bits. The format needs a function to tell if a contiguous entry
is dirty, and a function to clear a contiguous entry back to clean.

Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Samiullah Khawaja <skhawaja@google.com>
Tested-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
Tested-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>