configuration: system1: Add GPIO monitoring type

Some GPIOs do not support event_read method to monitor for value
changes. Added a new MonitorType field to specify if the GPIO
needs to be manually polled.

Tested:
- Verified no change when MonitorType not specified
- Verified functionality when Polling enum was specified

Change-Id: Ie5e8a2afe43d05192828292b629baade6b0c9c82
Signed-off-by: Chris Cain <cjcain@us.ibm.com>
diff --git a/schemas/legacy.json b/schemas/legacy.json
index 35624c1..22e1e5f 100644
--- a/schemas/legacy.json
+++ b/schemas/legacy.json
@@ -1164,6 +1164,9 @@
             },
             "Presence": {
                 "properties": {
+                    "MonitorType": {
+                        "enum": ["Event", "Polling"]
+                    },
                     "PinName": {
                         "type": "string"
                     },