iommufd/selftest: Add vIOMMU coverage for IOMMU_HWPT_INVALIDATE ioctl

iommufd/selftest: Add vIOMMU coverage for IOMMU_HWPT_INVALIDATE ioctl

Add a viommu_cache test function to cover vIOMMU invalidations using the
updated IOMMU_HWPT_INVALIDATE ioctl, which now allows passing in a vIOMMU
via its hwpt_id field.

Link: https://patch.msgid.link/r/f317f902041f3d05deaee4ca3fdd8ef4b8297361.1730836308.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>