Add support for READING in chunk mode.

In case the last SAVE command recognized that there was still some image
to be read, however, there was no available chunk to use for, this task
was delayed for the reader till one chunk will be consumed and becomes
available.

In the above case, a work will be executed to read in the background the
next image from the device.
Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20230911093856.81910-9-yishaih@nvidia.comSigned-off-by: Alex Williamson <alex.williamson@redhat.com>