spapr_nvdimm.c: make 'label-size' mandatory

spapr_nvdimm.c: make 'label-size' mandatory

The pseries machine does not support NVDIMM modules without label.
Attempting to do so, even if the overall block size is aligned with
256MB, will seg fault the guest kernel during NVDIMM probe. This
can be avoided by forcing 'label-size' to always be present for
sPAPR NVDIMMs.

The verification was put before the alignment check because the
presence of label-size affects the alignment calculation, so
it's not optimal to warn the user about an alignment error,
then about the lack of label-size, then about a new alignment
error when the user sets a label-size.

Signed-off-by: Daniel Henrique Barboza <[email protected]>
Message-Id: <20200413203628[email protected]>
Signed-off-by: David Gibson <[email protected]>