Add gNMI device state subscriber

Also disable some gNMI/P4-related BUCK files that break the BUCK build
for ONOS 1.14

Change-Id: I20cb5e130f4e416bf8678aab2e5268faf24ad06b
diff --git a/providers/general/BUILD b/providers/general/BUILD
index 0f4654f..2ac73a0 100644
--- a/providers/general/BUILD
+++ b/providers/general/BUILD
@@ -7,7 +7,7 @@
     category = "Provider",
     description = "General device southbound providers.",
     included_bundles = BUNDLES,
-    required_apps = [],
+    required_apps = ["org.onosproject.protocols.gnmi"],
     title = "General Device Provider",
     url = "http://onosproject.org",
 )