PEL: Add next level of support maintenance procedure

Maintenance procedures are part of the PEL callout section.
This procedure is indicates isolation not possible, contact
your next level of support.

Signed-off-by: Jayanth Othayoth <ojayanth@in.ibm.com>
Change-Id: If1d481604e411947e47cb7c9c20d79e938c65db3
diff --git a/extensions/openpower-pels/registry/schema/schema.json b/extensions/openpower-pels/registry/schema/schema.json
index fe42ff1..64b0ade 100644
--- a/extensions/openpower-pels/registry/schema/schema.json
+++ b/extensions/openpower-pels/registry/schema/schema.json
@@ -451,7 +451,7 @@
         {
             "description": "The maintenance procedure callout.",
             "type": "string",
-            "enum": ["bmc_code"]
+            "enum": ["bmc_code", "next_level_support"]
         },
 
         "useInventoryLocCode":