iommufd: Lock all IOAS objects

Define helpers to lock and unlock all IOAS objects.
This will allow DMA mappings to be updated atomically during live update.
This code is substantially the same as an initial version provided by
Jason, plus fixes.

Link: https://patch.msgid.link/r/1731527497-16091-3-git-send-email-steven.sistare@oracle.com


Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>