Extends iommufd_hw_pagetable_alloc() to accept user flags, the uAPI will
provide the flags.

Link: https://lore.kernel.org/r/20230928071528.26258-4-yi.l.liu@intel.comReviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Yi Liu <yi.l.liu@intel.com>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>