schemas: legacy: extract IpmbDevice

This allows to remove some properties from 'Aggregate' schema which are
no longer needed, since there is now a more specific schema to use.

Tested: Schema Validator Pass

Change-Id: Id8735de23d999d781f40a194e8fa8b6e24d978a8
Signed-off-by: Alexander Hansen <alexander.hansen@9elements.com>
diff --git a/schemas/global.json b/schemas/global.json
index f0f4715..31b40f5 100644
--- a/schemas/global.json
+++ b/schemas/global.json
@@ -100,6 +100,9 @@
                             "$ref": "legacy.json#/$defs/EmmcDevice"
                         },
                         {
+                            "$ref": "legacy.json#/$defs/IpmbDevice"
+                        },
+                        {
                             "$ref": "virtual_sensor.json#/$defs/VirtualSensor"
                         },
                         {