WFT Baseboard: Make some voltage sensors power on only

Add power on only flag.

Change-Id: Iaaa8c4889a79baeecf24834e6ae47ebc5510146b
Signed-off-by: James Feist <james.feist@linux.intel.com>
diff --git a/schemas/global.json b/schemas/global.json
index 8e0536b..fdf4f15 100644
--- a/schemas/global.json
+++ b/schemas/global.json
@@ -238,6 +238,9 @@
                             "Count": {
                                 "type": "integer"
                             },
+                            "PowerState": {
+                                "type": "string"
+                            },
                             "BindPresence": {
                                 "type": "string"
                             },