iommufd/selftest: Update hw_info coverage for an input data_type

iommufd/selftest: Update hw_info coverage for an input data_type

Test both IOMMU_HW_INFO_TYPE_DEFAULT and IOMMU_HW_INFO_TYPE_SELFTEST, and
add a negative test for an unsupported type.

Also drop the unused mask in test_cmd_get_hw_capabilities() as checkpatch
is complaining.

Link: https://patch.msgid.link/r/f01a1e50cd7366f217cbf192ad0b2b79e0eb89f0.1752126748.git.nicolinc@nvidia.com
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Reviewed-by: Pranjal Shrivastava <praan@google.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>