hw/block/nvme: Support Zone Descriptor Extensions

hw/block/nvme: Support Zone Descriptor Extensions

Zone Descriptor Extension is a label that can be assigned to a zone.
It can be set to an Empty zone and it stays assigned until the zone
is reset.

This commit adds a new optional module property,
"zoned.descr_ext_size". Its value must be a multiple of 64 bytes.
If this value is non-zero, it becomes possible to assign extensions
of that size to any Empty zones. The default value for this property
is 0, therefore setting extensions is disabled by default.

Signed-off-by: Hans Holmberg <hans.holmberg@wdc.com>
Signed-off-by: Dmitry Fomichev <dmitry.fomichev@wdc.com>
Reviewed-by: Niklas Cassel <Niklas.Cassel@wdc.com>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Klaus Jensen <k.jensen@samsung.com>