iommufd/selftest: Add IOMMU_TEST_OP_ACCESS_REPLACE_IOAS coverage

Add a new IOMMU_TEST_OP_ACCESS_REPLACE_IOAS to allow replacing the
access->ioas, corresponding to the iommufd_access_replace() helper.

Then add replace coverage as a part of user_copy test case, which
basically repeats the copy test after replacing the old ioas with a new
one.

Link: https://lore.kernel.org/r/a4897f93d41c34b972213243b8dbf4c3832842e4.1690523699.git.nicolinc@nvidia.com


Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>