schemas: legacy: refine 'Polling'

This property is only used in 2 boards:

- kudo_motherboard.json
- wft_baseboard.json

and i am not sure if it even works. Defining it anyways for
completeness.

Tested: Schema Validator Pass

Change-Id: I8364678edc901c479128a916dfbc19a2c86c605b
Signed-off-by: Alexander Hansen <alexander.hansen@9elements.com>
diff --git a/schemas/legacy.json b/schemas/legacy.json
index 3a424a3..e30beef 100644
--- a/schemas/legacy.json
+++ b/schemas/legacy.json
@@ -1066,7 +1066,22 @@
                 "enum": ["High", "Low"]
             },
             "Polling": {
-                "type": "object"
+                "type": "object",
+                "additionalProperties": false,
+                "properties": {
+                    "AveragingPeriod": {
+                        "type": "number"
+                    },
+                    "Interval": {
+                        "type": "number"
+                    },
+                    "PollRate": {
+                        "type": "number"
+                    },
+                    "Label": {
+                        "type": "string"
+                    }
+                }
             },
             "PowerFactorMax": {
                 "type": "number"