iommufd/device: Replace device_list with device_array

iommufd/device: Replace device_list with device_array

igroup->attach->device_list is used to track attached device of a group
in the RID path. Such tracking is also needed in the PASID path in order
to share path with the RID path.

While there is only one list_head in the iommufd_device. It cannot work
if the device has been attached in both RID path and PASID path. To solve
it, replacing the device_list with an xarray. The attached iommufd_device
is stored in the entry indexed by the idev->obj.id.

Link: https://patch.msgid.link/r/20250321171940.7213-9-yi.l.liu@intel.com
Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Yi Liu <yi.l.liu@intel.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>