Add 'utilization' to xyz.openbmc_project.Sensor.Value interface

Resource utilization is one of core type of metrics to observe.
While it's not a real-world physical property, this kind of sensor addresses
real-world needs of data-center administrators.

Adding 'utilization' namespace is crucial to extend existing metrics, like so:
- CPU temperature,
- CPU power,
- CPU utilization.

Change-Id: I65ed33917c025f7350a4b41cc2e22eadd458dbef
Signed-off-by: Adrian Ambrożewicz <adrian.ambrozewicz@linux.intel.com>
diff --git a/xyz/openbmc_project/Sensor/Value.interface.yaml b/xyz/openbmc_project/Sensor/Value.interface.yaml
index 5f42b92..53710e0 100644
--- a/xyz/openbmc_project/Sensor/Value.interface.yaml
+++ b/xyz/openbmc_project/Sensor/Value.interface.yaml
@@ -10,6 +10,7 @@
       current
       power
       energy
+      utilization
 
     Any service implementing Sensor.Value on one or more objects must
     implement org.freedesktop.DBus.ObjectManager on the sensors namespace root.
@@ -40,6 +41,7 @@
           For objects in the current namespace, Unit must be "Amperes".
           For objects in the power namespace, Unit must be "Watts".
           For objects in the energy namespace, Unit must be "Joules".
+          For objects in the utilization namespace, Unit must be "Percent"
     - name: Scale
       type: int64
       description: >
@@ -72,3 +74,6 @@
         - name: Joules
           description: >
             Energy transfer as Joules.
+        - name: Percent
+          description: >
+            Resource utilization as percentage.