iommufd/selftest: Test out_capabilities in IOMMU_GET_HW_INFO

Enumerate the capabilities from the mock device and test whether it
advertises as expected. Include it as part of the iommufd_dirty_tracking
fixture.

Link: https://lore.kernel.org/r/20231024135109.73787-18-joao.m.martins@oracle.com


Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>