Add support for SAVING in chunk mode, it includes running a work
that will fill the next chunk from the device.

In case the number of available chunks will reach the MAX_NUM_CHUNKS,
the next chunk SAVING will be delayed till the reader will consume one
chunk.

The next patch from the series will add the reader part of the chunk
mode.
Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20230911093856.81910-8-yishaih@nvidia.comSigned-off-by: Alex Williamson <alex.williamson@redhat.com>