Add prebuilt_platform_compat_config

It just provides the metadata needed by the global singleton as the
rest is in the apex.

Bug: 182402754
Test: m nothing
Change-Id: I511df7a3a06dab13ddb9ad63392ae5310dfee9c4

apex/apex.go

@@ -569,7 +569,7 @@ var (
 	executableTag   = dependencyTag{name: "executable", payload: true}
 	fsTag           = dependencyTag{name: "filesystem", payload: true}
 	bootImageTag    = dependencyTag{name: "bootImage", payload: true}
-	compatConfigTag = dependencyTag{name: "compatConfig", payload: true}
+	compatConfigTag = dependencyTag{name: "compatConfig", payload: true, sourceOnly: true}
 	javaLibTag      = dependencyTag{name: "javaLib", payload: true}
 	jniLibTag       = dependencyTag{name: "jniLib", payload: true}
 	keyTag          = dependencyTag{name: "key"}