Add parameters for external sensor

Adding Units, string type, to support ExternalSensor.

Adding MinReading. MaxReading was already included, but not MinReading,
so added it similarly.

Adding MinValue and MaxValue, similar to MinReading and MaxReading.
Unfortunately, these are used somewhat interchangeably in dbus-sensors,
and a separate change should later be used to standardize on one, going
forward, but this would break existing configurations in the field that
were using the other.

Signed-off-by: Josh Lehan <krellan@google.com>
Signed-off-by: Ed Tanous <edtanous@google.com>
Change-Id: Ia06ab6a3bf1c507e0a13826c212d90ba09b3edf7
diff --git a/schemas/legacy.json b/schemas/legacy.json
index 5e9fe82..73d513c 100644
--- a/schemas/legacy.json
+++ b/schemas/legacy.json
@@ -90,6 +90,18 @@
                 "MaxReading": {
                     "$ref": "#/definitions/Types/MaxReading"
                 },
+                "MaxValue": {
+                    "$ref": "#/definitions/Types/MaxValue"
+                },
+                "Units": {
+                    "$ref": "#/definitions/Types/Units"
+                },
+                "MinReading": {
+                    "$ref": "#/definitions/Types/MinReading"
+                },
+                "MinValue": {
+                    "$ref": "#/definitions/Types/MinValue"
+                },
                 "Name": {
                     "$ref": "#/definitions/Types/Name"
                 },
@@ -407,6 +419,18 @@
             "MaxReading": {
                 "type": "number"
             },
+            "MaxValue": {
+                "type": "number"
+            },
+            "Units": {
+                "type": "string"
+            },
+            "MinReading": {
+                "type": "number"
+            },
+            "MinValue": {
+                "type": "number"
+            },
             "Name": {
                 "type": "string"
             },