Contains a vendor specific estimate of the percentage of NVM subsystem
life used based on the actual usage and the manufacturer's prediction of NVM
life. A value of 100 indicates that the estimated endurance of the NVM in
the NVM subsystem has been consumed, but may not indicate an NVM subsystem
failure. The value is allowed to exceed 100. Percentages greater than 254
shall be represented as 255. This value shall be updated once per power-on
hour (when the controller is not in a sleep state).