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, "zone_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: Klaus Jensen <k.jensen@samsung.com>