Add PowerState Interface

There are many cases where a BMC would have to show the power state
of a FRU, This commit adds a generic interface for capturing the
power state of an object.

This would help map the actual power state of the FRU to redfish.
Below is the spec link :
http://redfish.dmtf.org/schemas/v1/Resource.json#/definitions/PowerState

Signed-off-by: Manojkiran Eda <manojkiran.eda@gmail.com>
Change-Id: Iea8455ef9b03de7923104c1e29d28a201756fc7a
diff --git a/yaml/xyz/openbmc_project/State/Decorator/PowerState.interface.yaml b/yaml/xyz/openbmc_project/State/Decorator/PowerState.interface.yaml
new file mode 100644
index 0000000..4f8ea2d
--- /dev/null
+++ b/yaml/xyz/openbmc_project/State/Decorator/PowerState.interface.yaml
@@ -0,0 +1,29 @@
+description: >
+    Implement to indicate the power state of the object
+properties:
+    - name: PowerState
+      type: enum[self.State]
+      default: Unknown
+      description: >
+        The current power status of the object.
+
+enumerations:
+  - name: State
+    description: >
+      Power state enum.
+    values:
+      - name: On
+        description: >
+         The state of the object is powered on.
+      - name: Off
+        description: >
+         The state of the object is powered off.
+      - name: PoweringOn
+        description: >
+         The object is in a temporary state between off and on.
+      - name: PoweringOff
+        description: >
+         The object is in a temporary state between on and off.
+      - name: Unknown
+        description: >
+         The power state is unknown.