iommufd: Introduce data struct for AMD nested domain allocation

iommufd: Introduce data struct for AMD nested domain allocation

Introduce IOMMU_HWPT_DATA_AMD_GUEST data type for IOMMU guest page table,
which is used for stage-1 in nested translation. The data structure
contains information necessary for setting up the AMD HW-vIOMMU support.

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
Reviewed-by: Vasant Hegde <vasant.hegde@amd.com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>