iommufd: Introduce IOMMUFD_OBJ_VIOMMU and its related struct

iommufd: Introduce IOMMUFD_OBJ_VIOMMU and its related struct

Add a new IOMMUFD_OBJ_VIOMMU with an iommufd_viommu structure to represent
a slice of physical IOMMU device passed to or shared with a user space VM.
This slice, now a vIOMMU object, is a group of virtualization resources of
a physical IOMMU's, such as:
 - Security namespace for guest owned ID, e.g. guest-controlled cache tags
 - Non-device-affiliated event reporting, e.g. invalidation queue errors
 - Access to a sharable nesting parent pagetable across physical IOMMUs
 - Virtualization of various platforms IDs, e.g. RIDs and others
 - Delivery of paravirtualized invalidation
 - Direct assigned invalidation queues
 - Direct assigned interrupts

Add a new viommu_alloc op in iommu_ops, for drivers to allocate their own
vIOMMU structures. And this allocation also needs a free(), so add struct
iommufd_viommu_ops.

To simplify a vIOMMU allocation, provide a iommufd_viommu_alloc() helper.
It's suggested that a driver should embed a core-level viommu structure in
its driver-level viommu struct and call the iommufd_viommu_alloc() helper,
meanwhile the driver can also implement a viommu ops:
    struct my_driver_viommu {
        struct iommufd_viommu core;
        /* driver-owned properties/features */
        ....
    };

    static const struct iommufd_viommu_ops my_driver_viommu_ops = {
        .free = my_driver_viommu_free,
        /* future ops for virtualization features */
        ....
    };

    static struct iommufd_viommu my_driver_viommu_alloc(...)
    {
        struct my_driver_viommu *my_viommu =
                iommufd_viommu_alloc(ictx, my_driver_viommu, core,
                                     my_driver_viommu_ops);
        /* Init my_viommu and related HW feature */
        ....
        return &my_viommu->core;
    }

    static struct iommu_domain_ops my_driver_domain_ops = {
        ....
        .viommu_alloc = my_driver_viommu_alloc,
    };

Link: https://patch.msgid.link/r/64685e2b79dea0f1dc56f6ede04809b72d578935.1730836219.git.nicolinc@nvidia.com
Suggested-by: Jason Gunthorpe <jgg@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>