The only case when sPAPR NVRAM migrates now is if is backed by a file and
copy-storage migration is performed. In other cases NVRAM does not
migrate regardless whether it is backed by a file or not.
This enables shadow copy of NVRAM in RAM which is read from a file
(if used) and used for reads. Writes to NVRAM are mirrored to the file.
This defines a VMSTATE descriptor for NVRAM device so the memory copy
of NVRAM can migrate and be flushed to a backing file on the destination
if one is specified.
Signed-off-by: Alexey Kardashevskiy <firstname.lastname@example.org>
Reviewed-by: David Gibson <email@example.com>
Signed-off-by: Alexander Graf <firstname.lastname@example.org>