Control.Power.Mode: Add errors to properties

Add two errors to the PowerMode property:
  NotAllowed - when the mode is not allowed to be set
  InvalidArgument - when the mode is not a valid value

Errors will be generated by openpower-occ-control

Tested on Rainier

Change-Id: Ifa8d7536d410ae0c369d65eeb58c45d26c65c254
Signed-off-by: Chris Cain <cjcain@us.ibm.com>
diff --git a/yaml/xyz/openbmc_project/Control/Power/Mode.interface.yaml b/yaml/xyz/openbmc_project/Control/Power/Mode.interface.yaml
index d7a707b..70a0365 100644
--- a/yaml/xyz/openbmc_project/Control/Power/Mode.interface.yaml
+++ b/yaml/xyz/openbmc_project/Control/Power/Mode.interface.yaml
@@ -9,6 +9,9 @@
           This property shall contain the computer system power mode setting.
           This defines the processor speed based on the priority of power
           consumption and performance.
+      errors:
+          - xyz.openbmc_project.Common.Error.InvalidArgument
+          - xyz.openbmc_project.Common.Error.NotAllowed
 
     - name: SafeMode
       type: boolean