configurations: yosemite4: Add PowerState to Medusa Board

To let psusensor get real value of MEDUSA_MBX_ sensors while
corresponding chassis power state is ON.
Add "SlotId" in schemas/legacy.json to indicate corresponding chassis
slot number.

Test plan:
1. Modify property "CurrentPowerState" to
xyz.openbmc_project.State.Chassis.PowerState.Off, the sensor value of
corresponding slot should be nan.
2. Change property "CurrentPowerState" to
xyz.openbmc_project.State.Chassis.PowerState.Off, the sensor value of
corresponding slot should be real value.

Change-Id: I2d3a5f33a6091b69cb6a78357692e6066a72dcbc
Signed-off-by: Bright Cheng <bright.cheng.wiwynn@gmail.com>
diff --git a/schemas/legacy.json b/schemas/legacy.json
index 683afed..37bf0b9 100644
--- a/schemas/legacy.json
+++ b/schemas/legacy.json
@@ -218,6 +218,9 @@
                 "SensorType": {
                     "$ref": "#/definitions/Types/SensorType"
                 },
+                "SlotId": {
+                    "$ref": "#/definitions/Types/SlotId"
+                },
                 "TachMaxPercent": {
                     "$ref": "#/definitions/Types/TachMaxPercent"
                 },
@@ -1041,6 +1044,9 @@
             "SensorType": {
                 "type": "string"
             },
+            "SlotId": {
+                "type": "string"
+            },
             "TachMaxPercent": {
                 "type": "number"
             },