iommufd/selftest: Add coverage for IOPF test

iommufd/selftest: Add coverage for IOPF test

Extend the selftest tool to add coverage of testing IOPF handling. This
would include the following tests:

- Allocating and destroying an iommufd fault object.
- Allocating and destroying an IOPF-capable HWPT.
- Attaching/detaching/replacing an IOPF-capable HWPT on a device.
- Triggering an IOPF on the mock device.
- Retrieving and responding to the IOPF through the file interface.

Link: https://lore.kernel.org/r/20240702063444.105814-11-baolu.lu@linux.intel.com
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>